With Intel TDX and AMD SEV-SNP for better securing virtual machines on the mainline Linux kernel, memory is accepted/initialized immediately at boot time by the VMs although the capability exists to have " unaccepted memory " where that memory is only dealt with by the VMs later on or on an as-needed basis. For two years now Intel engineers have been working on this unaccepted memory support and this week posted their thirteenth iteration of these fundamental Linux kernel patches.

The UEFI 2.9 specification introduces the notion of memory "acceptance" where memory needs to be accepted prior to being used by guest VMs. By not accepting the memory by VMs with the likes of TDX and SEV-SNP until needed, it lowers the boot time for VMs and also lowers memory overhead of the system.

Intel engineers working on the Linux kernel support for UEFI unaccepted memory have said that this functionality yields "substantially" lower boot times for VMs. Booting to a shell can be around 2.5x faster for a VM with 4G of RAM using Intel Trust Domain Extensions or around four times faster for an Intel TDX VM with 64G of memory.

The code being worked on by Intel is obviously focused on TDX while the core infrastructure can be reused by AMD SEV-SNP and the TDX-specific patches are separated.

With the v13 patches, there is a fix for some boot issues and other minor changes. It looks like work is settling down though so hopefully soon this UEFI unaccepted memory support will be picked up by the mainline Linux kernel. Those interested in the latest iteration of this unaccepted memory support can find it via this kernel mailing list thread .