Re: [PATCH v17 08/10] PM: hibernate: disable when there are active secretmem users

Michal Hocko
2021-02-08T10:57:21Z

On Mon 08-02-21 11:53:58, David Hildenbrand wrote:
> On 08.02.21 11:51, Michal Hocko wrote:
> > On Mon 08-02-21 11:32:11, David Hildenbrand wrote:
> > > On 08.02.21 11:18, Michal Hocko wrote:
> > > > On Mon 08-02-21 10:49:18, Mike Rapoport wrote:
> > > > > From: Mike Rapoport <rppt@linux.ibm.com>
> > > > >
> > > > > It is unsafe to allow saving of secretmem areas to the hibernation
> > > > > snapshot as they would be visible after the resume and this essentially
> > > > > will defeat the purpose of secret memory mappings.
> > > > >
> > > > > Prevent hibernation whenever there are active secret memory users.
> > > >
> > > > Does this feature need any special handling? As it is effectivelly
> > > > unevictable memory then it should behave the same as other mlock, ramfs
> > > > which should already disable hibernation as those cannot be swapped out,
> > > > no?
> > > >
> > >
> > > Why should unevictable memory not go to swap when hibernating? We're merely
> > > dumping all of our system RAM (including any unmovable allocations) to swap
> > > storage and the system is essentially completely halted.
> > >
> > My understanding is that mlock is never really made visible via swap
> > storage.
>
> "Using swap storage for hibernation" and "swapping at runtime" are two
> different things. I might be wrong, though.

Well, mlock is certainly used to keep sensitive information, not only to
protect from major/minor faults.
--
Michal Hocko
SUSE Labs