Re: [PATCH v1 1/4] mm/memory_hotplug: use "unsigned long" for PFN in zone_for_pfn_range()

[David Hildenbrand]

On 14.07.21 22:13, Heiko Carstens wrote:
> On Mon, Jul 12, 2021 at 02:40:49PM +0200, David Hildenbrand wrote:
> > Checkpatch complained on a follow-up patch that we are using "unsigned"
> > here, which defaults to "unsigned int" and checkpatch is correct.
> >
> > Use "unsigned long" instead, just as we do in other places when handling
> > PFNs. This can bite us once we have physical addresses in the range of
> > multiple TB.
> >
> > Fixes: e5e689302633 ("mm, memory_hotplug: display allowed zones in the preferred ordering")
> > Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
> > ---
> >   include/linux/memory_hotplug.h | 4 ++--
> >   mm/memory_hotplug.c            | 4 ++--
> >   2 files changed, 4 insertions(+), 4 deletions(-)
>
> I'd propose to add Cc: <stable@xxxxxxxxxxxxxxx> since I actually had
> the fun to try to debug something like this a couple of years ago:
> 6cdb18ad98a4 ("mm/vmstat: fix overflow in mod_zone_page_state()")

Good point, and thinking again what can go wrong, I tend to agree. We 
are trying to keep zones contiguous and it could happen that we end up 
with something like ZONE_DMA here (via default_kernel_zone_for_pfn()) 
and would consequently online something to ZONE_DMA that doesn't belong 
there, resulting in crashes.

@Andrew can you add  Cc: <stable@xxxxxxxxxxxxxxx> and

"As we will search for a fitting zone using the wrong pfn, we might end 
up onlining memory to one of the special kernel zones, such as ZONE_DMA, 
which can end badly as the onlined memory does not satisfy properties of 
these zones."

Thanks Heiko!

--
Thanks,

David / dhildenb