Re: [PATCH 4/6] mm: hugetlb_vmemmap: add missing smp_wmb() before set_pte_at()

[Muchun Song]

> On Aug 22, 2022, at 16:45, Miaohe Lin <linmiaohe@xxxxxxxxxx> wrote:
> 
> On 2022/8/20 16:12, Muchun Song wrote:
>> 
>> 
>>> On Aug 16, 2022, at 21:05, Miaohe Lin <linmiaohe@xxxxxxxxxx> 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
> 
>