Fix PSCI CPU ON race when setting state to ON_PENDING
When a CPU is powered down using PSCI CPU OFF API, it disables its caches
and updates its `aff_info_state` to OFF. The corresponding cache line is
invalidated by the CPU so that the update will be observed by other CPUs
running with caches enabled. There is a possibility that another CPU
which has been trying to turn ON this CPU via PSCI CPU ON API,
has already seen the update to `aff_info_state` and proceeds to update
the state to ON_PENDING prior to the cache invalidation. This may result
in the update of the state to ON_PENDING being discarded.
This patch fixes this issue by making sure that the update of `aff_info_state`
to ON_PENDING sticks by reading back the value after the cache flush and
retrying it if not updated. The patch also adds a dsbish() to
`psci_do_cpu_off()` to ensure ordering of the update to `aff_info_state`
prior to cache line invalidation.
Fixes ARM-software/tf-issues#349
Change-Id: I225de99957fe89871f8c57bcfc243956e805dcca
diff --git a/services/std_svc/psci/psci_off.c b/services/std_svc/psci/psci_off.c
index 9ed6f0c..cef6668 100644
--- a/services/std_svc/psci/psci_off.c
+++ b/services/std_svc/psci/psci_off.c
@@ -129,10 +129,13 @@
* Set the affinity info state to OFF. This writes directly to
* main memory as caches are disabled, so cache maintenance is
* required to ensure that later cached reads of aff_info_state
- * return AFF_STATE_OFF.
+ * return AFF_STATE_OFF. A dsbish() ensures ordering of the
+ * update to the affinity info state prior to cache line
+ * invalidation.
*/
flush_cpu_data(psci_svc_cpu_data.aff_info_state);
psci_set_aff_info_state(AFF_STATE_OFF);
+ dsbish();
inv_cpu_data(psci_svc_cpu_data.aff_info_state);
/*