linux-kernel - [ANNOUNCE] PUCK Notes - 2024.01.03

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Message-ID: <20240103174343.3016720-1-seanjc@google.com>
Date: Wed,  3 Jan 2024 09:43:43 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Paolo Bonzini <pbonzini@...hat.com>, James Houghton <jthoughton@...gle.com>, 
	Peter Xu <peterx@...hat.com>, Axel Rasmussen <axelrasmussen@...gle.com>, 
	Oliver Upton <oliver.upton@...ux.dev>, David Matlack <dmatlack@...gle.com>, 
	Aaron Lewis <aaronlewis@...gle.com>, Isaku Yamahata <isaku.yamahata@...ux.intel.com>, 
	Yan Zhao <yan.y.zhao@...el.com>, Marc Zyngier <maz@...nel.org>
Subject: [ANNOUNCE] PUCK Notes - 2024.01.03 - Post-copy for guest_memfd()

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.