On Tue, May 18, 2021 at 02:01:36PM -0400, Peter Xu wrote: > > > Indeed it'll be odd for a COW page since for COW page then it means after > > > parent/child writting to the page it'll clone into two, then it's a mistery on > > > which one will be the one that "exclusived owned" by the device.. > > > > For COW pages it is like every other fork case.. We can't reliably > > write-protect the device_exclusive page during fork so we must copy it > > at fork time. > > > > Thus three reasonable choices: > > - Copy to a new CPU page > > - Migrate back to a CPU page and write protect it > > - Copy to a new device exclusive page > > IMHO the ownership question would really help us to answer this one.. I'm confused about what device ownership you are talking about It is just a page and it is tied to some specific pgmap? If the thing providing the migration stuff goes away then all device_exclusive pages should revert back to CPU pages and destroy the pgmap? Jason
