[ANNOUNCE] PUCK Notes - 2024.01.03 - Post-copy for guest_memfd()

[Sean Christopherson]

Recording and slides of the post-copy for guest_memfd discussion:

  https://drive.google.com/corp/drive/folders/1_3bLYrR7oYZ06XvOPY_xZGUApGhq-j3W?resourcekey=0-0C1BYqhodcNvHFIqVwKMTg

Key takeaways:

 - There is no known use case for tying "data invalid" to the guest_memfd
   inode, i.e. letting each "view" (struct file / struct kvm / VM) control its
   own behavior is acceptable, and arguably desirable as it provides userspace
   more flexibility.

 - If the "data invalid" attribute is tied to a given view, then routing the
   ioctl() through KVM provides a superset of functionality compared to making
   a guest_memfd specific ioctl(), e.g. KVM can apply the attribute to any gfn
   regardless of backing store.

 - Pursuing a fully generic file-based solution is undesirable as there are a
   large number of questions that need answers, and there is no known use case
   beyond KVM to drive those discussions.

Feel free to chime in with anything important that I missed.