linux-kernel - Re: [PATCH v2] mm/swapfile: unuse_pte can map random data if swap read fails

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Date:   Wed, 20 Apr 2022 14:21:27 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     Peter Xu <peterx@...hat.com>
CC:     <akpm@...ux-foundation.org>, <willy@...radead.org>,
        <vbabka@...e.cz>, <dhowells@...hat.com>, <neilb@...e.de>,
        <david@...hat.com>, <apopple@...dia.com>, <surenb@...gle.com>,
        <minchan@...nel.org>, <sfr@...b.auug.org.au>,
        <rcampbell@...dia.com>, <naoya.horiguchi@....com>,
        <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] mm/swapfile: unuse_pte can map random data if swap
 read fails

On 2022/4/20 5:36, Peter Xu wrote:
> On Sat, Apr 16, 2022 at 11:05:49AM +0800, Miaohe Lin wrote:
>> @@ -1797,6 +1797,17 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
>>  		goto out;
>>  	}
>>  
>> +	if (unlikely(!PageUptodate(page))) {
>> +		pte_t pteval;
>> +
>> +		dec_mm_counter(vma->vm_mm, MM_SWAPENTS);
>> +		pteval = swp_entry_to_pte(make_swapin_error_entry(page));
>> +		set_pte_at(vma->vm_mm, addr, pte, pteval);
>> +		swap_free(entry);
>> +		ret = 0;
>> +		goto out;
>> +	}
>> +
>>  	/* See do_swap_page() */
>>  	BUG_ON(!PageAnon(page) && PageMappedToDisk(page));
>>  	BUG_ON(PageAnon(page) && PageAnonExclusive(page));
> 
> Totally off-topic, but.. today when I was looking at the unuse path I just
> found that the swp bits could have got lost for either soft-dirty and
> uffd-wp here?  A quick patch attached.

Am I supposed to test-and-send this patch? The patch looks good to me except the
build error pointed out by kernel test robot.

> 
> Maybe at some point we should start to have some special helpers for
> set_pte_at() when we're converting between present/non-present ptes, so as
> to make sure all these will always be taken care of properly.

That will be helpful. There are many places doing the similar thing.

> 

Thanks!