From: Steven Price <steven.price@arm.com>
To: Christophe Leroy <christophe.leroy@csgroup.eu>,
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: Mon, 19 Apr 2021 15:00:14 +0100 [thread overview]
Message-ID: <4a76fbda-aa9d-867b-e2eb-a1951780aeec@arm.com> (raw)
In-Reply-To: <627ee414-2f78-94e3-b77b-1013f52e77e3@csgroup.eu>
On 19/04/2021 14:14, 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 :
>>>> On 15/04/2021 18:18, Christophe Leroy wrote:
>>>>
>>>> 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 ;)
>>
>
> 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
> the pgtable referred by the PMD entry. But what happens if that PMD
> entry is referring another pgtable which is inside the same page as
> kasan_early_shadow_pte ?
>
> Shouldn't the test be
>
> if (pmd_page_vaddr(val) == lm_alias(kasan_early_shadow_pte))
> return note_kasan_page_table(walk, addr);
Now I come to look at this code again, I think you're right. On arm64
this doesn't cause a problem - page tables are page sized and page
aligned, so there couldn't be any non-KASAN pgtables sharing the page.
Obviously that's not necessarily true of other architectures.
Feel free to add a patch to your series ;)
Steve
WARNING: multiple messages have this Message-ID (diff)
From: Steven Price <steven.price@arm.com>
To: Christophe Leroy <christophe.leroy@csgroup.eu>,
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: Mon, 19 Apr 2021 15:00:14 +0100 [thread overview]
Message-ID: <4a76fbda-aa9d-867b-e2eb-a1951780aeec@arm.com> (raw)
In-Reply-To: <627ee414-2f78-94e3-b77b-1013f52e77e3@csgroup.eu>
On 19/04/2021 14:14, 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 :
>>>> On 15/04/2021 18:18, Christophe Leroy wrote:
>>>>
>>>> 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 ;)
>>
>
> 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
> the pgtable referred by the PMD entry. But what happens if that PMD
> entry is referring another pgtable which is inside the same page as
> kasan_early_shadow_pte ?
>
> Shouldn't the test be
>
> if (pmd_page_vaddr(val) == lm_alias(kasan_early_shadow_pte))
> return note_kasan_page_table(walk, addr);
Now I come to look at this code again, I think you're right. On arm64
this doesn't cause a problem - page tables are page sized and page
aligned, so there couldn't be any non-KASAN pgtables sharing the page.
Obviously that's not necessarily true of other architectures.
Feel free to add a patch to your series ;)
Steve
_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv
WARNING: multiple messages have this Message-ID (diff)
From: Steven Price <steven.price@arm.com>
To: Christophe Leroy <christophe.leroy@csgroup.eu>,
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: Mon, 19 Apr 2021 15:00:14 +0100 [thread overview]
Message-ID: <4a76fbda-aa9d-867b-e2eb-a1951780aeec@arm.com> (raw)
In-Reply-To: <627ee414-2f78-94e3-b77b-1013f52e77e3@csgroup.eu>
On 19/04/2021 14:14, 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 :
>>>> On 15/04/2021 18:18, Christophe Leroy wrote:
>>>>
>>>> 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 ;)
>>
>
> 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
> the pgtable referred by the PMD entry. But what happens if that PMD
> entry is referring another pgtable which is inside the same page as
> kasan_early_shadow_pte ?
>
> Shouldn't the test be
>
> if (pmd_page_vaddr(val) == lm_alias(kasan_early_shadow_pte))
> return note_kasan_page_table(walk, addr);
Now I come to look at this code again, I think you're right. On arm64
this doesn't cause a problem - page tables are page sized and page
aligned, so there couldn't be any non-KASAN pgtables sharing the page.
Obviously that's not necessarily true of other architectures.
Feel free to add a patch to your series ;)
Steve
WARNING: multiple messages have this Message-ID (diff)
From: Steven Price <steven.price@arm.com>
To: Christophe Leroy <christophe.leroy@csgroup.eu>,
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: Mon, 19 Apr 2021 15:00:14 +0100 [thread overview]
Message-ID: <4a76fbda-aa9d-867b-e2eb-a1951780aeec@arm.com> (raw)
In-Reply-To: <627ee414-2f78-94e3-b77b-1013f52e77e3@csgroup.eu>
On 19/04/2021 14:14, 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 :
>>>> On 15/04/2021 18:18, Christophe Leroy wrote:
>>>>
>>>> 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 ;)
>>
>
> 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
> the pgtable referred by the PMD entry. But what happens if that PMD
> entry is referring another pgtable which is inside the same page as
> kasan_early_shadow_pte ?
>
> Shouldn't the test be
>
> if (pmd_page_vaddr(val) == lm_alias(kasan_early_shadow_pte))
> return note_kasan_page_table(walk, addr);
Now I come to look at this code again, I think you're right. On arm64
this doesn't cause a problem - page tables are page sized and page
aligned, so there couldn't be any non-KASAN pgtables sharing the page.
Obviously that's not necessarily true of other architectures.
Feel free to add a patch to your series ;)
Steve
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2021-04-19 14:00 UTC|newest]
Thread overview: 91+ 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 ` Christophe Leroy
2021-04-15 17:18 ` Christophe Leroy
2021-04-15 17:18 ` Christophe Leroy
2021-04-15 17:18 ` [PATCH v1 1/5] mm: pagewalk: Fix walk for hugepage tables Christophe Leroy
2021-04-15 17:18 ` Christophe Leroy
2021-04-15 17:18 ` Christophe Leroy
2021-04-15 17:18 ` Christophe Leroy
2021-04-15 22:43 ` Daniel Axtens
2021-04-15 22:43 ` Daniel Axtens
2021-04-15 22:43 ` Daniel Axtens
2021-04-15 22:43 ` Daniel Axtens
2021-04-16 5:48 ` Christophe Leroy
2021-04-16 5:48 ` Christophe Leroy
2021-04-16 5:48 ` Christophe Leroy
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 ` Christophe Leroy
2021-04-15 17:18 ` Christophe Leroy
2021-04-15 17:18 ` Christophe Leroy
2021-04-15 17:18 ` [PATCH v1 3/5] mm: ptdump: Provide page size to notepage() Christophe Leroy
2021-04-15 17:18 ` Christophe Leroy
2021-04-15 17:18 ` Christophe Leroy
2021-04-15 17:18 ` Christophe Leroy
2021-04-15 23:12 ` Daniel Axtens
2021-04-15 23:12 ` Daniel Axtens
2021-04-15 23:12 ` Daniel Axtens
2021-04-15 23:12 ` Daniel Axtens
2021-04-16 5:19 ` Christophe Leroy
2021-04-16 5:19 ` Christophe Leroy
2021-04-16 5:19 ` Christophe Leroy
2021-04-16 5:19 ` Christophe Leroy
2021-04-16 9:28 ` Steven Price
2021-04-16 9:28 ` Steven Price
2021-04-16 9:28 ` Steven Price
2021-04-16 9:28 ` Steven Price
2021-04-16 10:38 ` Christophe Leroy
2021-04-16 10:38 ` Christophe Leroy
2021-04-16 10:38 ` Christophe Leroy
2021-04-16 10:38 ` Christophe Leroy
2021-04-16 10:51 ` Steven Price
2021-04-16 10:51 ` Steven Price
2021-04-16 10:51 ` Steven Price
2021-04-16 10:51 ` Steven Price
2021-04-16 11:08 ` Christophe Leroy
2021-04-16 11:08 ` Christophe Leroy
2021-04-16 11:08 ` Christophe Leroy
2021-04-16 11:08 ` Christophe Leroy
2021-04-16 13:00 ` Steven Price
2021-04-16 13:00 ` Steven Price
2021-04-16 13:00 ` Steven Price
2021-04-16 13:00 ` Steven Price
2021-04-16 14:40 ` Christophe Leroy
2021-04-16 14:40 ` Christophe Leroy
2021-04-16 14:40 ` Christophe Leroy
2021-04-16 14:40 ` Christophe Leroy
2021-04-16 15:04 ` Christophe Leroy
2021-04-16 15:04 ` Christophe Leroy
2021-04-16 15:04 ` Christophe Leroy
2021-04-16 15:15 ` Christophe Leroy
2021-04-16 15:15 ` Christophe Leroy
2021-04-16 15:15 ` Christophe Leroy
2021-04-16 16:00 ` Steven Price
2021-04-16 16:00 ` Steven Price
2021-04-16 16:00 ` Steven Price
2021-04-19 13:14 ` Christophe Leroy
2021-04-19 13:14 ` Christophe Leroy
2021-04-19 13:14 ` Christophe Leroy
2021-04-19 13:14 ` Christophe Leroy
2021-04-19 14:00 ` Steven Price [this message]
2021-04-19 14:00 ` Steven Price
2021-04-19 14:00 ` Steven Price
2021-04-19 14:00 ` Steven Price
2021-04-19 16:41 ` Christophe Leroy
2021-04-19 16:41 ` Christophe Leroy
2021-04-19 16:41 ` Christophe Leroy
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 17:18 ` Christophe Leroy
2021-04-15 17:18 ` Christophe Leroy
2021-04-15 17:18 ` Christophe Leroy
2021-04-15 23:29 ` Daniel Axtens
2021-04-15 23:29 ` Daniel Axtens
2021-04-15 23:29 ` Daniel Axtens
2021-04-16 5:25 ` Christophe Leroy
2021-04-16 5:25 ` Christophe Leroy
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
2021-04-15 17:18 ` Christophe Leroy
2021-04-15 17:18 ` Christophe Leroy
2021-04-15 17:18 ` Christophe Leroy
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