[ANNOUNCE] PUCK Notes - 2024.04.03 - TDX Upstreaming Strategy

[Sean Christopherson]

 - Recording and slides uploaded[1].

 - Hold off on v20 for a few weeks, to try and land as much prep work as
   possible before v20.

 - Exactly how to slice n' dice the series to make it easier to review is TBD,
   but generally speaking the plan is to queue patches into a "dead" branch,
   e.g. kvm/kvm-coco-queue, when they are ready, to reduce the sheer volume of
   the series and thus help alleviate reviewer fatigue.

 - Don't hardcode fixed/required CPUID values in KVM, use available metadata
   from TDX Module to reject "bad" guest CPUID (or let the TDX module reject?).
   I.e. don't let a guest silently run with a CPUID that diverges from what
   userspace provided.

 - Ideally, the TDX Module would come with full metadata (not in JSON format)
   that KVM can (a) use to reject a "bad" CPUID configuration (from userspace),
   and (b) that KVM can provide to userspace to make debugging issues suck less.

 - For guest MAXPHYADDR vs. GPAW, rely on KVM_GET_SUPPORTED_CPUID to enumerate
   the usable MAXPHYADDR[2], and simply refuse to enable TDX if the TDX Module
   isn't compatible.  Specifically, if MAXPHYADDR=52, 5-level paging is enabled,
   but the TDX-Module only allows GPAW=0, i.e. only supports 4-level paging.

[1] https://drive.google.com/corp/drive/folders/1hm_ITeuB6DjT7dNd-6Ezybio4tRRQOlC
[2] https://lore.kernel.org/all/20240313125844.912415-1-kraxel@xxxxxxxxxx