Actually the current version allows you to delay the allocation to a later time (e.g. page fault time) if you don't call fallocate() on the private fd. fallocate() is necessary in previous versions because we treat the existense in the fd as 'private' but in this version we track private/shared info in KVM so we don't rely on that fact from memory backstores.
Does this also mean reservation of guest physical memory with secure processor (both for SEV-SNP & TDX) will also happen at page fault time?
Do we plan to keep it this way?
If you are talking about accepting memory by the guest, it is initiated by the guest and has nothing to do with page fault time vs fallocate() allocation of host memory. I mean acceptance happens after host memory allocation but they are not in lockstep, acceptance can happen much later.
No, I meant reserving guest physical memory range from hypervisor e.g with RMPUpdate for SEV-SNP or equivalent at TDX side (PAMTs?).
Thanks, Pankaj