x86/sgx: Log information when a node lacks an EPC section

For optimized performance, firmware typically distributes EPC sections
evenly across different NUMA nodes. However, there are scenarios where
a node may have both CPUs and memory but no EPC section configured. For
example, in an 8-socket system with a Sub-Numa-Cluster=2 setup, there
are a total of 16 nodes. Given that the maximum number of supported EPC
sections is 8, it is simply not feasible to assign one EPC section to
each node. This configuration is not incorrect - SGX will still operate
correctly; it is just not optimized from a NUMA standpoint.

For this reason, log a message when a node with both CPUs and memory
lacks an EPC section. This will provide users with a hint as to why they
might be experiencing less-than-ideal performance when running SGX
enclaves.

Suggested-by: Dave Hansen <[email protected]>
Signed-off-by: Aaron Lu <[email protected]>
Signed-off-by: Dave Hansen <[email protected]>
Reviewed-by: Jarkko Sakkinen <[email protected]>
Acked-by: Kai Huang <[email protected]>
Link: https://lore.kernel.org/all/20240905080855.1699814-3-aaron.lu%40intel.com

Author: Aaron Lu

arch/x86/kernel/cpu/sgx/main.c

@@ -848,6 +848,13 @@ static bool __init sgx_page_cache_init(void)
 		return false;
 	}
 
+	for_each_online_node(nid) {
+		if (!node_isset(nid, sgx_numa_mask) &&
+		    node_state(nid, N_MEMORY) && node_state(nid, N_CPU))
+			pr_info("node%d has both CPUs and memory but doesn't have an EPC section\n",
+				nid);
+	}
+
 	return true;
 }