checkpoint/restore: Adding more "Getters" to the KVM API

[scalingtree]

Hi lists,

(Re-sending as plain text.)

We are in the process of using an external tool (CRIU) to checkpoint/restore a 
KVM-enabled virtual machine. Initially we target the hypervisor kvmtool but the 
extension, if done well, should allow to checkpoint any hypervisor: like Qemu 
or firecracker.

CRIU can checkpoint and restore most of the application (or the VMM in our 
case) state except the state of the kernel module KVM. To overcome this 
limitation, we need more getters in the KVM API to extract the state of the VM.

One example of a missing getter is the one for the guest memory. There is a 
KVM_SET_MEMORY API call. But there is no equivalent getter: KVM_GET_MEMORY. 

Can we add such getters to the KVM API? Any idea of the difficulty? I think one 
of the difficulties will be to get the state of the architecture-specific state 
of KVM: for now, we are targetting Intel x86_64 architecture (VT-X).

Any feedback will be appreciated.

Best Regards,
ScalingTree