Re: [PATCH] powerpc: Perform a bounds check in arch_add_memory

From: Alastair D'Silva
Date: Tue Aug 27 2019 - 02:40:07 EST

On Tue, 2019-08-27 at 08:28 +0200, Michal Hocko wrote:
> On Tue 27-08-19 15:20:46, Alastair D'Silva wrote:
> > From: Alastair D'Silva <alastair@xxxxxxxxxxx>
> >
> > It is possible for firmware to allocate memory ranges outside
> > the range of physical memory that we support (MAX_PHYSMEM_BITS).
> Doesn't that count as a FW bug? Do you have any evidence of that in
> the
> field? Just wondering...

Not outside our lab, but OpenCAPI attached LPC memory is assigned
addresses based on the slot/NPU it is connected to. These addresses
prior to:
4ffe713b7587 ("powerpc/mm: Increase the max addressable memory to 2PB")
were inaccessible and resulted in bogus sections - see our discussion
on 'mm: Trigger bug on if a section is not found in __section_nr'.
Doing this check here was your suggestion :)

It's entirely possible that a similar problem will occur in the future,
and it's cheap to guard against, which is why I've added this.

Alastair D'Silva
Open Source Developer
Linux Technology Centre, IBM Australia
mob: 0423 762 819