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?
Having an uffd-wp mode that doesn't require pre-population would really
be great. I remember you shared prototypes.
--
Thanks,
David / dhildenb
