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Subject: Re: [PATCH v5] mm/gup: check page hwposion status for coredump.
From:   David Hildenbrand <david@redhat.com>
To:     Aili Yao <yaoaili@kingsoft.com>,
        Matthew Wilcox <willy@infradead.org>,
        akpm@linux-foundation.org, naoya.horiguchi@nec.com
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        yangfeng1@kingsoft.com, sunhao2@kingsoft.com,
        Oscar Salvador <osalvador@suse.de>,
        Mike Kravetz <mike.kravetz@oracle.com>
References: <20210317163714.328a038d@alex-virtual-machine>
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 <20210319104437.6f30e80d@alex-virtual-machine>
 <20210320003516.GC3420@casper.infradead.org>
 <20210322193318.377c9ce9@alex-virtual-machine>
 <afeac310-c6aa-f9d8-6c90-e7e7f21ddf9a@redhat.com>
Organization: Red Hat GmbH
Message-ID: <f316ca3b-6f09-c51d-9661-66171f14ee33@redhat.com>
Date:   Fri, 26 Mar 2021 15:22:49 +0100
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On 26.03.21 15:09, David Hildenbrand wrote:
> On 22.03.21 12:33, Aili Yao wrote:
>> When we do coredump for user process signal, this may be one SIGBUS signal
>> with BUS_MCEERR_AR or BUS_MCEERR_AO code, which means this signal is
>> resulted from ECC memory fail like SRAR or SRAO, we expect the memory
>> recovery work is finished correctly, then the get_dump_page() will not
>> return the error page as its process pte is set invalid by
>> memory_failure().
>>
>> But memory_failure() may fail, and the process's related pte may not be
>> correctly set invalid, for current code, we will return the poison page,
>> get it dumped, and then lead to system panic as its in kernel code.
>>
>> So check the hwpoison status in get_dump_page(), and if TRUE, return NULL.
>>
>> There maybe other scenario that is also better to check hwposion status
>> and not to panic, so make a wrapper for this check, Thanks to David's
>> suggestion(<david@redhat.com>).
>>
>> Link: https://lkml.kernel.org/r/20210319104437.6f30e80d@alex-virtual-machine
>> Signed-off-by: Aili Yao <yaoaili@kingsoft.com>
>> Cc: David Hildenbrand <david@redhat.com>
>> Cc: Matthew Wilcox <willy@infradead.org>
>> Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
>> Cc: Oscar Salvador <osalvador@suse.de>
>> Cc: Mike Kravetz <mike.kravetz@oracle.com>
>> Cc: Aili Yao <yaoaili@kingsoft.com>
>> Cc: stable@vger.kernel.org
>> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
>> ---
>>    mm/gup.c      |  4 ++++
>>    mm/internal.h | 20 ++++++++++++++++++++
>>    2 files changed, 24 insertions(+)
>>
>> diff --git a/mm/gup.c b/mm/gup.c
>> index e4c224c..6f7e1aa 100644
>> --- a/mm/gup.c
>> +++ b/mm/gup.c
>> @@ -1536,6 +1536,10 @@ struct page *get_dump_page(unsigned long addr)
>>    				      FOLL_FORCE | FOLL_DUMP | FOLL_GET);
>>    	if (locked)
>>    		mmap_read_unlock(mm);
> 
> Thinking again, wouldn't we get -EFAULT from __get_user_pages_locked()
> when stumbling over a hwpoisoned page?
> 
> See __get_user_pages_locked()->__get_user_pages()->faultin_page():
> 
> handle_mm_fault()->vm_fault_to_errno(), which translates
> VM_FAULT_HWPOISON to -EFAULT, unless FOLL_HWPOISON is set (-> -EHWPOISON)
> 
> ?

Or doesn't that happen as you describe "But memory_failure() may fail, 
and the process's related pte may not be correctly set invalid" -- but 
why does that happen?

On a similar thought, should get_user_pages() never return a page that 
has HWPoison set? E.g., check also for existing PTEs if the page is 
hwpoisoned?

@Naoya, Oscar

-- 
Thanks,

David / dhildenb