linux-kernel - Re: [PATCH v5] mm/gup: check page hwposion status for coredump.

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Date:   Wed, 31 Mar 2021 09:05:06 +0200
From:   David Hildenbrand <david@...hat.com>
To:     HORIGUCHI NAOYA(堀口 直也) 
        <naoya.horiguchi@....com>, Matthew Wilcox <willy@...radead.org>
Cc:     Aili Yao <yaoaili@...gsoft.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "yangfeng1@...gsoft.com" <yangfeng1@...gsoft.com>,
        "sunhao2@...gsoft.com" <sunhao2@...gsoft.com>,
        Oscar Salvador <osalvador@...e.de>,
        Mike Kravetz <mike.kravetz@...cle.com>
Subject: Re: [PATCH v5] mm/gup: check page hwposion status for coredump.

On 31.03.21 08:53, HORIGUCHI NAOYA(堀口 直也) wrote:
> On Wed, Mar 31, 2021 at 07:07:39AM +0100, Matthew Wilcox wrote:
>> On Wed, Mar 31, 2021 at 01:52:59AM +0000, HORIGUCHI NAOYA(堀口 直也) wrote:
>>> If we successfully unmapped but failed in truncate_error_page() for example,
>>> the processes mapping the page would get -EFAULT as expected.  But even in
>>> this case, other processes could reach the error page via page cache and
>>> __get_user_pages_locked() for them could return the hwpoisoned page.
>>
>> How would that happen?  We check PageHWPoison before inserting a page
>> into the page tables.  See, eg, filemap_map_pages() and __do_fault().
> 
> Ah, you're right, that never happens. I misread the code.
> Thanks for correcting me.
> 

I'm wondering if there is a small race window, if we poison a page while 
inserting it.

-- 
Thanks,

David / dhildenb