On Tue, May 18, 2021 at 01:27:42PM -0400, Peter Xu wrote: > I also have a pure and high level question regarding a process fork() when > there're device exclusive ptes: would the two processes then own the device > together? Is this a real usecase? If the pages are MAP_SHARED then yes. All VMAs should point at the same device_exclusive page and all VMA should migrate back to CPU pages together. > 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 Jason
