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

[Dan Williams]

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?