On Fri, Sep 03, 2021 at 09:58:06AM +0200, David Hildenbrand wrote: > > > That'll be good enough for live snapshot as uffd-wp works for zero pages, > > > however I'm just afraid it may stop working for some new users of it when > > > zero > > > pages won't suffice. > > > > I thought about that as well. But snapshots/migration will read all > > memory either way and consume real memory when there is no shared zero > > page. So it's just shifting the point in time when we allocate all these > > pages I guess. > > ... thinking again, even when populating on shmem and friends there is > nothing stopping pages from getting mapped out again. > > What would happen when trying uffd-wp protection on a pte_none() in your > current shmem implementation? Will it lookup if there is something in the > page cache (not a hole) and set a PTE marker? Or will it simply skip as > there is currently nothing in the page table? Or will it simply > unconditionally install a PTE marker, even if there is a hole?
It (will - I haven't rebased and posted) sets a pte marker. So uffd-wp will always work on read prefault irrelevant of memory type in the future. > > Having an uffd-wp mode that doesn't require pre-population would really be > great. I remember you shared prototypes. Yes, I planned to do that after the shmem bits, because they have some conflict. I don't want to mess up more with the current series either, which is already hard to push, which is very unfortunate. -- Peter Xu
