vm_compute_max_gfn
uint64_t max_gfn = vm_compute_max_gfn(vm);
gpa_base = ((vm_compute_max_gfn(vm) + 1) * vm->page_size) - sz;
unsigned long vm_compute_max_gfn(struct kvm_vm *vm);
vm->max_gfn = vm_compute_max_gfn(vm);