Hello, On Sat, Jan 09, 2021 at 07:44:35PM -0500, Andrea Arcangeli wrote: > allowing a child to corrupt memory in the parent. That's a problem > that could happen not-maliciously too. So the scenario described I updated the above partly quoted sentence since in the previous version it didn't have full accuracy: https://git.kernel.org/pub/scm/linux/kernel/git/andrea/aa.git/commit/?id=fc5a76b1c14e5e6cdc64ece306fc03773662d98a "However since a single transient GUP pin on a tail page, would elevate the page_count for all other tail pages (unlike the mapcount which is subpage granular), the COW page reuse inaccuracy would then cross different vmas and the effect would happen at a distance in vma of different processes. A single GUP pin taken on a subpage mapped in a different process could trigger 511 false positive COWs copies in the local process, after a fork()." This a best effort to try to document all side effects, but it'd be great to hear from Kirill too on the above detail to have confirmation. Thanks and have a great weekend everyone, Andrea
