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

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Message-ID: <6cf3726c-d6d0-4255-2deb-3688227c633e@huawei.com>
Date:   Wed, 20 Apr 2022 14:15:02 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     Alistair Popple <apopple@...dia.com>
CC:     <akpm@...ux-foundation.org>, <willy@...radead.org>,
        <vbabka@...e.cz>, <dhowells@...hat.com>, <neilb@...e.de>,
        <david@...hat.com>, <surenb@...gle.com>, <minchan@...nel.org>,
        <peterx@...hat.com>, <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 8:25, Alistair Popple wrote:
> Miaohe Lin <linmiaohe@...wei.com> writes:
> 
>> On 2022/4/19 15:53, Alistair Popple wrote:
>>> Also in madvise_free_pte_range() you could just remove the swap entry as it's no
>>> longer needed.
>>>
>>
>> This swap entry will be removed in madvise_dontneed_single_vma().
>> And in madvise_free_pte_range(), we may need to keep it as same as
>> hwpoison entry. Or am I supposed to remove it even if hwpoison entry
>> is reused later?
> 
> Why would we need to keep it for MADV_FREE though? It only works on private
> anonymous memory, and once the MADV_FREE operation has succeeded callers can
> expect they might get zero-fill pages if accessing the memory again. Therefore
> it should be safe to delete the entry. I think that applies equally to a
> hwpoison entry too - there's no reason to kill the process if it has called
> MADV_FREE on the range.

I tend to agree. We can drop the swapin error entry and hwpoison entry when MADV_FREE
is called. Should I squash these into the current patch or a separate one is preferred?

Thanks for your suggestion!

> 
>>
>> Thanks!
>>
>>> Alistair Popple <apopple@...dia.com> writes:
>>>
>>>> Miaohe Lin <linmiaohe@...wei.com> writes:
>>>>
>> ...