Merge pull request #1033 from davidcunado-arm/dc/psci_flush

Address edge case for stale PSCI CPU data in cache

lib/psci/psci_on.c

@@ -64,7 +64,20 @@ int psci_cpu_on_start(u_register_t target_cpu,
 	/*
 	 * Generic management: Ensure that the cpu is off to be
 	 * turned on.
+	 * Perform cache maintanence ahead of reading the target CPU state to
+	 * ensure that the data is not stale.
+	 * There is a theoretical edge case where the cache may contain stale
+	 * data for the target CPU data - this can occur under the following
+	 * conditions:
+	 * - the target CPU is in another cluster from the current
+	 * - the target CPU was the last CPU to shutdown on its cluster
+	 * - the cluster was removed from coherency as part of the CPU shutdown
+	 *
+	 * In this case the cache maintenace that was performed as part of the
+	 * target CPUs shutdown was not seen by the current CPU's cluster. And
+	 * so the cache may contain stale data for the target CPU.
 	 */
+	flush_cpu_data_by_index(target_idx, psci_svc_cpu_data.aff_info_state);
 	rc = cpu_on_validate_state(psci_get_aff_info_state_by_idx(target_idx));
 	if (rc != PSCI_E_SUCCESS)
 		goto exit;