dat_get_storage_key
int dat_get_storage_key(union asce asce, gfn_t gfn, union skey *skey);
r = dat_get_storage_key(kvm->arch.gmap->asce, gpa_to_gfn(gpa), &storage_key);
r = dat_get_storage_key(vcpu->arch.gmap->asce, gpa_to_gfn(gpa), &storage_key);
r = dat_get_storage_key(kvm->arch.gmap->asce,
r = dat_get_storage_key(asce, gfn, &skey);
rc = dat_get_storage_key(vcpu->arch.gmap->asce, gpa_to_gfn(gaddr), &key);