On 14.07.21 22:13, Heiko Carstens wrote:

On Mon, Jul 12, 2021 at 02:40:49PM +0200, David Hildenbrand wrote:

quoted

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 <redacted>
---
  include/linux/memory_hotplug.h | 4 ++--
  mm/memory_hotplug.c            | 4 ++--
  2 files changed, 4 insertions(+), 4 deletions(-)

I'd propose to add Cc: [off-list ref] 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: [off-list ref] 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