x86/domctl: Make XEN_DOMCTL_set_address_size singleshot
Toolstacks (including some out-of-tree ones) use XEN_DOMCTL_set_address_size
at most once per domain, and it ends up having a destructive effect on the
available CPUID policy for a domain.
To avoid ordering issues between altering the policy via domctl, and the
constructive effects which would have to happen from switching back to native,
explicitly reject this case.
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>