There is rather large ecosystem of tooling for poking and peeking the insides of VMs, usually called "VMI" (virtual machine introspection). kvm-vmi is one such example, but there are many others https://github.com/KVM-VMI/kvm-vmi
There's a library [1] that implements message passing and locking for communiction between VMs in a similar way and is used by the awesome looking glass project to send the accelerated GPU video stream from a vm to the host or a different vm.
Its a 2021 tutorial that describes how to configure qemu to share memory between a host process and a qemu machine through /dev/shm.