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Subject: Re: [PATCH] mm/hugetlb: avoid corrupting page->mapping in
 hugetlb_mcopy_atomic_pte
To:     Mike Kravetz <mike.kravetz@oracle.com>
CC:     <akpm@linux-foundation.org>, <songmuchun@bytedance.com>,
        Axel Rasmussen <axelrasmussen@google.com>,
        Peter Xu <peterx@redhat.com>, <linux-mm@kvack.org>,
        <linux-kernel@vger.kernel.org>
References: <20220712130542.18836-1-linmiaohe@huawei.com>
 <Ys2xyCUnqpJt0eIo@monkey>
From:   Miaohe Lin <linmiaohe@huawei.com>
Message-ID: <1f9e8378-f61c-5bfe-1c47-fbaf0dc4f51a@huawei.com>
Date:   Wed, 13 Jul 2022 10:10:56 +0800
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On 2022/7/13 1:39, Mike Kravetz wrote:
> On 07/12/22 21:05, Miaohe Lin wrote:
>> In MCOPY_ATOMIC_CONTINUE case with a non-shared VMA, pages in the page
>> cache are installed in the ptes. But hugepage_add_new_anon_rmap is called
>> for them mistakenly because they're not vm_shared. This will corrupt the
>> page->mapping used by page cache code.
>>
>> Fixes: f619147104c8 ("userfaultfd: add UFFDIO_CONTINUE ioctl")
>> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
>> ---
>>  mm/hugetlb.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> This looks correct to me.
> 
> Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>

Many thanks for review.

> 
> However, I am having a hard time wrapping my head around how UFFDIO_CONTINUE
> should work on non-anon private mappings.  For example, a private mapping of
> a hugetlbfs file.  I think we just map the page in the file/cache and do not
> set the write bit in the pte.  So, yes we would want page_dup_file_rmap()
> in this case as shown below.

+1

> 
> Adding Axel and Peter on Cc: as they were more involved in adding that code
> and the design of UFFDIO_CONTINUE.

That would be really helpful.

Thanks.

>