linux-kernel - Re: [PATCH 4/6] mm: hugetlb_vmemmap: add missing smp_wmb() before set_pte

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Date:   Mon, 22 Aug 2022 16:45:16 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     Muchun Song <muchun.song@...ux.dev>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Muchun Song <songmuchun@...edance.com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/6] mm: hugetlb_vmemmap: add missing smp_wmb() before
 set_pte_at()

On 2022/8/20 16:12, Muchun Song wrote:
> 
> 
>> On Aug 16, 2022, at 21:05, Miaohe Lin <linmiaohe@...wei.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?

Thanks,
Miaohe Lin