CA-422187: safer defaults for global claims

Xen may have already allocated some memory for the domain, and the overhead is
only an estimate.
A global claim failing is a hard failure, so instead use a more conservative
estimate: `memory.build_start_mib`.
This is similar to `required_host_free_mib`, but doesn't take overhead into
account.

Eventually we'd want to have another argument to the create hypercall that
tells it what NUMA node(s) to use, and then we can include all the overhead too
there.

Fixes: 060d792 ("CA-422188: either always use claims or never use claims")

Signed-off-by: Edwin Török <[email protected]>

Author: edwintorok

ocaml/xenopsd/xc/domain.ml

@@ -1114,7 +1114,7 @@ let build_pre ~xc ~xs ~vcpus ~memory ~hard_affinity domid =
                 Xenops_server.cores_of_numa_affinity_policy pin ~vcpus
               in
               let memory =
-                Int64.(mul memory.required_host_free_mib (shift_left 1L 20))
+                Int64.(mul memory.build_start_mib (shift_left 1L 20))
               in
               match numa_placement domid ~vcpus ~cores ~memory affinity with
               | None ->