TSP: Allow preemption of synchronous S-EL1 interrupt handling
Earlier the TSP only ever expected to be preempted during Standard SMC
processing. If a S-EL1 interrupt triggered while in the normal world, it
will routed to S-EL1 `synchronously` for handling. The `synchronous` S-EL1
interrupt handler `tsp_sel1_intr_entry` used to panic if this S-EL1 interrupt
was preempted by another higher priority pending interrupt which should be
handled in EL3 e.g. Group0 interrupt in GICv3.
With this patch, the `tsp_sel1_intr_entry` now expects `TSP_PREEMPTED` as the
return code from the `tsp_common_int_handler` in addition to 0 (interrupt
successfully handled) and in both cases it issues an SMC with id
`TSP_HANDLED_S_EL1_INTR`. The TSPD switches the context and returns back
to normal world. In case a higher priority EL3 interrupt was pending, the
execution will be routed to EL3 where interrupt will be handled. On return
back to normal world, the pending S-EL1 interrupt which was preempted will
get routed to S-EL1 to be handled `synchronously` via `tsp_sel1_intr_entry`.
Change-Id: I2087c7fedb37746fbd9200cdda9b6dba93e16201
diff --git a/services/spd/tspd/tspd_main.c b/services/spd/tspd/tspd_main.c
index 4c4861d..4b89425 100644
--- a/services/spd/tspd/tspd_main.c
+++ b/services/spd/tspd/tspd_main.c
@@ -89,18 +89,22 @@
assert(ns_cpu_context);
/*
- * Restore non-secure state. The secure system
- * register context will be saved when required.
+ * To allow Secure EL1 interrupt handler to re-enter TSP while TSP
+ * is preempted, the secure system register context which will get
+ * overwritten must be additionally saved. This is currently done
+ * by the TSPD S-EL1 interrupt handler.
+ */
+
+ /*
+ * Restore non-secure state.
*/
cm_el1_sysregs_context_restore(NON_SECURE);
cm_set_next_eret_context(NON_SECURE);
/*
- * We need to restore non secure context according to
- * the SEL1 context which got preempted and currently
- * TSP can only be preempted when a STD SMC is ongoing.
- * Return SMC_PREEMPTED in x0 and restore non secure
- * context.
+ * The TSP was preempted during STD SMC execution.
+ * Return back to the normal world with SMC_PREEMPTED as error
+ * code in x0.
*/
SMC_RET1(ns_cpu_context, SMC_PREEMPTED);
}
@@ -327,7 +331,8 @@
/*
* This function ID is used only by the TSP to indicate that it has
- * finished handling a S-EL1 interrupt. Execution should resume
+ * finished handling a S-EL1 interrupt or was preempted by a higher
+ * priority pending EL3 interrupt. Execution should resume
* in the normal world.
*/
case TSP_HANDLED_S_EL1_INTR: