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

[Miaohe Lin]

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!