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Subject: Re: [PATCH] mm/hugetlb: avoid corrupting page->mapping in
 hugetlb_mcopy_atomic_pte
To:     Andrew Morton <akpm@linux-foundation.org>
CC:     <mike.kravetz@oracle.com>, <songmuchun@bytedance.com>,
        <linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>,
        Axel Rasmussen <axelrasmussen@google.com>,
        Peter Xu <peterx@redhat.com>
References: <20220712130542.18836-1-linmiaohe@huawei.com>
 <20220713102357.8328614813db01b569650ffd@linux-foundation.org>
From:   Miaohe Lin <linmiaohe@huawei.com>
Message-ID: <a47922cf-eb30-1ad9-fc96-1896254564ef@huawei.com>
Date:   Thu, 14 Jul 2022 17:59:53 +0800
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On 2022/7/14 1:23, Andrew Morton wrote:
> On Tue, 12 Jul 2022 21:05:42 +0800 Miaohe Lin <linmiaohe@huawei.com> 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.
> 
> Well that sounds bad.  And theories on why this has gone unnoticed for
> over a year?  I assume this doesn't have coverage in our selftests?

As discussed in another thread, when minor fault handling is proposed, only
VM_SHARED vma is expected to be supported. And the test case is also missing.

Thanks.

> 
>> --- a/mm/hugetlb.c
>> +++ b/mm/hugetlb.c
>> @@ -6038,7 +6038,7 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm,
>>  	if (!huge_pte_none_mostly(huge_ptep_get(dst_pte)))
>>  		goto out_release_unlock;
>>  
>> -	if (vm_shared) {
>> +	if (page_in_pagecache) {
>>  		page_dup_file_rmap(page, true);
>>  	} else {
>>  		ClearHPageRestoreReserve(page);
>> -- 
>> 2.23.0
> .
>