From: Christophe Leroy <christophe.leroy@csgroup.eu>
To: Steven Price <steven.price@arm.com>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>,
Michael Ellerman <mpe@ellerman.id.au>,
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
Subject: Re: [PATCH v1 3/5] mm: ptdump: Provide page size to notepage()
Date: Fri, 16 Apr 2021 12:38:18 +0200 [thread overview]
Message-ID: <da53d2f2-b472-0c38-bdd5-99c5a098675d@csgroup.eu> (raw)
In-Reply-To: <41819925-3ee5-4771-e98b-0073e8f095cf@arm.com>
Le 16/04/2021 à 11:28, Steven Price a écrit :
> 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 <christophe.leroy@csgroup.eu>
>> ---
>> arch/arm64/mm/ptdump.c | 2 +-
>> arch/riscv/mm/ptdump.c | 2 +-
>> arch/s390/mm/dump_pagetables.c | 3 ++-
>> arch/x86/mm/dump_pagetables.c | 2 +-
>> include/linux/ptdump.h | 2 +-
>> mm/ptdump.c | 16 ++++++++--------
>> 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_walk *walk,
>> {
>> struct ptdump_state *st = walk->private;
>> - st->note_page(st, addr, 4, pte_val(kasan_early_shadow_pte[0]));
>> + st->note_page(st, addr, 4, pte_val(kasan_early_shadow_pte[0]), PAGE_SIZE);
>
> I'm not completely sure what the page_size is going to be used for, but note that KASAN presents an
> interesting case here. We short-cut by detecting it's a KASAN region at a high level
> (PGD/P4D/PUD/PMD) and instead of walking the tree down just call note_page() *once* but with
> level==4 because we know KASAN sets up the page table like that.
>
> However the one call actually covers a much larger region - so while PAGE_SIZE matches the level it
> 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
CONFIG_KASAN_VMALLOC selected. In this situation, since
https://github.com/torvalds/linux/commit/af3d0a686 we don't have any common shadow page table anymore.
I'll test again without CONFIG_KASAN_VMALLOC.
>
> 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/
Christophe
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next prev parent reply other threads:[~2021-04-16 10:39 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-15 17:18 [PATCH v1 0/5] Convert powerpc to GENERIC_PTDUMP Christophe Leroy
2021-04-15 17:18 ` [PATCH v1 1/5] mm: pagewalk: Fix walk for hugepage tables Christophe Leroy
2021-04-15 22:43 ` Daniel Axtens
2021-04-16 5:48 ` Christophe Leroy
2021-04-15 17:18 ` [PATCH v1 2/5] mm: ptdump: Fix build failure Christophe Leroy
2021-04-15 17:18 ` [PATCH v1 3/5] mm: ptdump: Provide page size to notepage() Christophe Leroy
2021-04-15 23:12 ` Daniel Axtens
2021-04-16 5:19 ` Christophe Leroy
2021-04-16 9:28 ` Steven Price
2021-04-16 10:38 ` Christophe Leroy [this message]
2021-04-16 10:51 ` Steven Price
2021-04-16 11:08 ` Christophe Leroy
2021-04-16 13:00 ` Steven Price
2021-04-16 14:40 ` Christophe Leroy
2021-04-16 15:04 ` Christophe Leroy
2021-04-16 15:15 ` Christophe Leroy
2021-04-16 16:00 ` Steven Price
2021-04-19 13:14 ` Christophe Leroy
2021-04-19 14:00 ` Steven Price
2021-04-19 16:41 ` Christophe Leroy
2021-04-15 17:18 ` [PATCH v1 4/5] mm: ptdump: Support hugepd table entries Christophe Leroy
2021-04-15 23:29 ` Daniel Axtens
2021-04-16 5:25 ` Christophe Leroy
2021-04-15 17:18 ` [PATCH v1 5/5] powerpc/mm: Convert powerpc to GENERIC_PTDUMP Christophe Leroy
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