On Fri, Jun 6, 2025 at 9:25 AM Peter Xu <peterx@xxxxxxxxxx> wrote: > On Thu, Jun 05, 2025 at 05:11:53PM -0400, Tal Zussman wrote: > > > > As I mentioned in my response to James, it seems like the existing behavior > > is broken as well, due to the following in in userfaultfd_unregister(): > > > > if (!vma_can_userfault(cur, cur->vm_flags, wp_async)) > > goto out_unlock; > > > > where wp_async is derived from ctx, not cur. > > > > Pasting here: > > > > This also seems to indicate that the current behavior is broken and may reject > > unregistering some VMAs incorrectly. For example, a file-backed VMA registered > > with `wp_async` and UFFD_WP cannot be unregistered through a VMA that does not > > have `wp_async` set. > > This is true. Meanwhile it seems untrivial to fix the flag alone with the > prior per-vma loop to check compatibility. We could drop the prior check > but then it slightly breaks the abi in another way.. > > Then let's go with the change to see our luck. > > Could you mention more things when repost in the commit log? (1) wp_async > bug, (2) explicitly mention that this is a slight ABI change, and (3) not > needed to backport to stable. Will do! > Thanks, > > -- > Peter Xu >
