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SubjectRe: [PATCH 4/6] mm: hugetlb_vmemmap: add missing smp_wmb() before set_pte_at()
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> On Aug 22, 2022, at 16:45, Miaohe Lin <linmiaohe@huawei.com> wrote:
>
> On 2022/8/20 16:12, Muchun Song wrote:
>>
>>
>>> On Aug 16, 2022, at 21:05, Miaohe Lin <linmiaohe@huawei.com> wrote:
>>>
>>> The memory barrier smp_wmb() is needed to make sure that preceding stores
>>> to the page contents become visible before the below set_pte_at() write.
>>
>> I found another place where is a similar case. See kasan_populate_vmalloc_pte() in
>> mm/kasan/shadow.c.
>
> Thanks for your report.
>
>>
>> Should we fix it as well?
>
> I'm not familiar with kasan yet, but I think memory barrier is needed here or memory corrupt
> can't be detected until the contents are visible. smp_mb__after_atomic before set_pte_at should
> be enough? What's your opinion?

I didn’t see any atomic operation between set_pte_at() and memset(), I don’t think
smp_mb__after_atomic() is feasible if we really need to insert a barrier. I suggest
you to send a RFC patch to KASAN maintainers, they are more familiar with this than
us.

Thanks.

>
> Thanks,
> Miaohe Lin
>
>

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