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

[David Hildenbrand]

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.

As I mentioned, we would have to temporarily map in order to copy. 
Mapping it somewhere else (like kmap), outside of the direct map might 
reduce possible attacks.

--
Thanks,

David / dhildenb