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Passing things back with a spinlock held feels > pretty icky though, and obviously a no-go for a FOLL_PIN. Perhaps for a > FOLL_GET this would be workable. I didn't look closely at the ptrace code but maybe it would work to lock the folio and pass back a locked folio. Interacting with the PTLs to make the lock reliable. It is the logical inverse of the code I pointed to for inserting a folio into the page table. (but I've never looked at the folio lock or how the FSs use it, so don't belive me on this) Another interesting idea would be to use mm/pagewalk.c to implement the memory copy fully under the PTLs. Jason