Re: [PATCH 3/3] mm/sparsemem: avoid memmap overwrite for non-SPARSEMEM_VMEMMAP

[Wei Yang]

On Thu, Feb 06, 2020 at 06:06:54PM -0800, Dan Williams wrote:
>On Thu, Feb 6, 2020 at 3:17 PM Wei Yang <richardw.yang@xxxxxxxxxxxxxxx> wrote:
>>
>> In case of SPARSEMEM, populate_section_memmap() would allocate memmap
>> for the whole section, even we just want a sub-section. This would lead
>> to memmap overwrite if we a sub-section to an already populated section.
>>
>> Just return the populated memmap for non-SPARSEMEM_VMEMMAP case.
>>
>> Fixes: ba72b4c8cf60 ("mm/sparsemem: support sub-section hotplug")
>> Signed-off-by: Wei Yang <richardw.yang@xxxxxxxxxxxxxxx>
>> CC: Dan Williams <dan.j.williams@xxxxxxxxx>
>> ---
>>  mm/sparse.c | 10 ++++++++++
>>  1 file changed, 10 insertions(+)
>>
>> diff --git a/mm/sparse.c b/mm/sparse.c
>> index 56816f653588..c75ca40db513 100644
>> --- a/mm/sparse.c
>> +++ b/mm/sparse.c
>> @@ -836,6 +836,16 @@ static struct page * __meminit section_activate(int nid, unsigned long pfn,
>>         if (nr_pages < PAGES_PER_SECTION && early_section(ms))
>>                 return pfn_to_page(pfn);
>>
>> +       /*
>> +        * If it is not SPARSEMEM_VMEMMAP, we always populate memmap for the
>> +        * whole section, even for a sub-section.
>> +        *
>> +        * Return its memmap if already populated to avoid memmap overwrite.
>> +        */
>> +       if (!IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP) &&
>> +               valid_section(ms))
>> +               return __section_mem_map_addr(ms);
>
>Again, is check_pfn_span() failing to prevent this path?

Oh, you are right. Thanks

-- 
Wei Yang
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