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

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.