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 ovearhead into
account.

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

@@ -1063,7 +1063,7 @@ 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 ->