linux-kernel - Re: [PATCH v1] makedumpfile: exclude pages that are logically offline

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Date:   Wed, 21 Nov 2018 16:35:31 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Kazuhito Hagio <k-hagio@...jp.nec.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        kexec-ml <kexec@...ts.infradead.org>,
        "pv-drivers@...are.com" <pv-drivers@...are.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH v1] makedumpfile: exclude pages that are logically offline

On 21.11.18 15:58, Kazuhito Hagio wrote:
> Hi David,
> 
>> Linux marks pages that are logically offline via a page flag (map count).
>> Such pages e.g. include pages infated as part of a balloon driver or
>> pages that were not actually onlined when onlining the whole section.
>>
>> While the hypervisor usually allows to read such inflated memory, we
>> basically read and dump data that is completely irrelevant. Also, this
>> might result in quite some overhead in the hypervisor. In addition,
>> we saw some problems under Hyper-V, whereby we can crash the kernel by
>> dumping, when reading memory of a partially onlined memory segment
>> (for memory added by the Hyper-V balloon driver).
>>
>> Therefore, don't read and dump pages that are marked as being logically
>> offline.
>>
>> Signed-off-by: David Hildenbrand <david@...hat.com>
>> ---
>>  makedumpfile.c | 34 ++++++++++++++++++++++++++++++----
>>  makedumpfile.h |  1 +
>>  2 files changed, 31 insertions(+), 4 deletions(-)
>>
>> diff --git a/makedumpfile.c b/makedumpfile.c
>> index 8923538..b8bfd4c 100644
>> --- a/makedumpfile.c
>> +++ b/makedumpfile.c
>> @@ -88,6 +88,7 @@ mdf_pfn_t pfn_cache_private;
>>  mdf_pfn_t pfn_user;
>>  mdf_pfn_t pfn_free;
>>  mdf_pfn_t pfn_hwpoison;
>> +mdf_pfn_t pfn_offline;
>>
>>  mdf_pfn_t num_dumped;
>>
>> @@ -249,6 +250,21 @@ isHugetlb(unsigned long dtor)
>>                      && (SYMBOL(free_huge_page) == dtor));
>>  }
>>
>> +static int
>> +isOffline(unsigned long flags, unsigned int _mapcount)
>> +{
>> +	if (NUMBER(PAGE_BUDDY_MAPCOUNT_VALUE) == NOT_FOUND_NUMBER)
>> +		return FALSE;
> 
> This is NUMBER(PAGE_OFFLINE_MAPCOUNT_VALUE), isn't it?
> If so, I will correct it when merging.
> 
> Otherwise, looks good to me.
> 
> Thanks!
> Kazu

Indeed,

I will most probably resend either way along with a new mm series!

Thanks a lot!


-- 

Thanks,

David / dhildenb