[PATCH v1 3/5] mm: ptdump: Provide page size to notepage()
steven.price at arm.com
Mon Apr 19 15:00:14 BST 2021
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
>>> 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
>> 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 ;)
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