Messages in this thread | | | Date | Tue, 18 May 2021 14:33:34 -0300 | From | Jason Gunthorpe <> | Subject | Re: [PATCH v8 5/8] mm: Device exclusive memory access |
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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
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