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, 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
Subject: Re: [PATCH v1 3/5] mm: ptdump: Provide page size to notepage()
Date: Fri, 16 Apr 2021 17:15:23 +0200 [thread overview]
Message-ID: <10adad00-14de-61b6-ce2a-bdde23a34bcf@csgroup.eu> (raw)
In-Reply-To: <b245cf06-f2e5-87a5-9a5e-64efc39d415a@csgroup.eu>
Le 16/04/2021 à 17:04, Christophe Leroy a écrit :
>
>
> Le 16/04/2021 à 16:40, Christophe Leroy a écrit :
>>
>>
>> Le 16/04/2021 à 15:00, Steven Price a écrit :
>>> On 16/04/2021 12:08, 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 :
>>>>>>> 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 ;)
>>>>>
>>>>
>>>> Yes ... and no.
>>>>
>>>> It looks like the generic ptdump handles the case when several pgdir entries points to the same
>>>> kasan_early_shadow_pte. But it doesn't take into account the powerpc case where we have regular
>>>> 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 you have a similar check for
>>> 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 and it's going to cause
>>> problems in the future.
>>>
>>
>> I'm trying. I reverted the two commits b00ff6d8c and cabe8138.
>>
>> At the moment, I don't get exactly what I expect: For linear memory I get one line for each 8M
>> page whereas before reverting the patches I got one 16M line and one 112M line.
>>
>> And for KASAN shadow area I get two lines for the 2x 8M pages shadowing linear mem then I get one
>> 4M line for each PGDIR entry pointing to kasan_early_shadow_pte.
>>
>> 0xf8000000-0xf87fffff 0x07000000 8M huge rw present
>> 0xf8800000-0xf8ffffff 0x07800000 8M huge rw present
>> 0xf9000000-0xf93fffff 0x01430000 4M r present
> ...
>> 0xfec00000-0xfeffffff 0x01430000 4M r present
>>
>> Any idea ?
>>
>
>
> I think the different with other architectures is here:
>
> } else if (flag != st->current_flags || level != st->level ||
> addr >= st->marker[1].start_address ||
> pa != st->last_pa + PAGE_SIZE) {
>
>
> In addition to the checks everyone do, powerpc also checks "pa != st->last_pa + PAGE_SIZE".
> And it is definitely for that test that page_size argument add been added.
By replacing that test by (pa - st->start_pa != addr - st->start_address) it works again. So we
definitely don't need the real page size.
>
> I see that other architectures except RISCV don't dump the physical address. But even RISCV doesn't
> include that check.
>
> That physical address dump was added by commit aaa229529244 ("powerpc/mm: Add physical address to
> 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
_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv
next prev parent reply other threads:[~2021-04-16 15:16 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
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 [this message]
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=10adad00-14de-61b6-ce2a-bdde23a34bcf@csgroup.eu \
--to=christophe.leroy@csgroup.eu \
--cc=akpm@linux-foundation.org \
--cc=benh@kernel.crashing.org \
--cc=linux-arch@vger.kernel.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=linux-riscv@lists.infradead.org \
--cc=linux-s390@vger.kernel.org \
--cc=linuxppc-dev@lists.ozlabs.org \
--cc=mpe@ellerman.id.au \
--cc=paulus@samba.org \
--cc=steven.price@arm.com \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).