Re: [PATCH v16 07/11] secretmem: use PMD-size pages to amortize direct map fragmentation

Michal Hocko
2021-02-02T14:32:35Z

On Tue 02-02-21 15:26:20, David Hildenbrand wrote:
> On 02.02.21 15:22, Michal Hocko wrote:
> > On Tue 02-02-21 15:12:21, David Hildenbrand wrote:
> > [...]
> > > I think secretmem behaves much more like longterm GUP right now
> > > ("unmigratable", "lifetime controlled by user space", "cannot go on
> > > CMA/ZONE_MOVABLE"). I'd either want to reasonably well control/limit it or
> > > make it behave more like mlocked pages.
> >
> > I thought I have already asked but I must have forgotten. Is there any
> > actual reason why the memory is not movable? Timing attacks?
>
> I think the reason is simple: no direct map, no copying of memory.

This is an implementation detail though and not something terribly hard
to add on top later on. I was more worried there would be really
fundamental reason why this is not possible. E.g. security implications.
--
Michal Hocko
SUSE Labs