On Thu, Sep 24, 2020 at 04:29:03PM +0300, Mike Rapoport wrote: > From: Mike Rapoport <rppt@xxxxxxxxxxxxx> > > Removing a PAGE_SIZE page from the direct map every time such page is > allocated for a secret memory mapping will cause severe fragmentation of > the direct map. This fragmentation can be reduced by using PMD-size pages > as a pool for small pages for secret memory mappings. > > Add a gen_pool per secretmem inode and lazily populate this pool with > PMD-size pages. What's the actual efficacy of this? Since the pmd is per inode, all I need is a lot of inodes and we're in business to destroy the directmap, no? Afaict there's no privs needed to use this, all a process needs is to stay below the mlock limit, so a 'fork-bomb' that maps a single secret page will utterly destroy the direct map. I really don't like this, at all. IIRC Kirill looked at merging the directmap. I think he ran into performance issues there, but we really need something like that before something like this lands.
