Can the hypervisor and VMs share memory?

I was wondering if modifying the KVM would allow the hypervisor and VM to share memory.

I've been studying SEV, AMD's memory encryption technology, and this question came up.Is it possible for the hypervisor and VM to share memory?I don't have a detailed knowledge of KVM, so I can only guess.

I can imagine the following ways.

1. modify the KVM so that some of the memory for the VM to use is shared memory
2. pre-allocate shared memory on the host and modify KVM to allow the VM to use that memory

I wonder if the above 2 methods are possible.If it is, it would be possible to use SEV-SNP's VMPL feature to control the hypervisor's access to shared memory.