TSPD: Explicitly allow NS preemption for Yielding SMCs

When EL3 exception handling is in effect (i.e.,
EL3_EXCEPTION_HANDLING=1), Non-secure interrupts can't preempt Secure
execution. However, for yielding SMCs, preemption by Non-secure
interupts is intended.

This patch therefore adds a call to ehf_allow_ns_preemption() before
dispatching a Yielding SMC to TSP.

Change-Id: Ia3a1ae252f3adc0f14e6d7e0502f251bdb349bdf
Signed-off-by: Jeenu Viswambharan <[email protected]>

diff --git a/services/spd/tspd/tspd_main.c b/services/spd/tspd/tspd_main.c
index 2ba9f84c050e74b777e511a5fe4eec2f1a5177b0..c564f8b8670a5b26c0cb192b5529929705bcfbbc 100644 (file)
--- a/services/spd/tspd/tspd_main.c
+++ b/services/spd/tspd/tspd_main.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013-2017, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2013-2018, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -20,6 +20,7 @@
 #include <bl_common.h>
 #include <context_mgmt.h>
 #include <debug.h>
+#include <ehf.h>
 #include <errno.h>
 #include <platform.h>
 #include <runtime_svc.h>
@@ -540,6 +541,18 @@ uint64_t tspd_smc_handler(uint32_t smc_fid,
                                 */
                                enable_intr_rm_local(INTR_TYPE_NS, SECURE);
 #endif
+
+#if EL3_EXCEPTION_HANDLING
+                               /*
+                                * With EL3 exception handling, while an SMC is
+                                * being processed, Non-secure interrupts can't
+                                * preempt Secure execution. However, for
+                                * yielding SMCs, we want preemption to happen;
+                                * so explicitly allow NS preemption in this
+                                * case.
+                                */
+                               ehf_allow_ns_preemption();
+#endif
                        }
 
                        cm_el1_sysregs_context_restore(SECURE);
@@ -646,7 +659,13 @@ uint64_t tspd_smc_handler(uint32_t smc_fid,
                enable_intr_rm_local(INTR_TYPE_NS, SECURE);
 #endif
 
-
+#if EL3_EXCEPTION_HANDLING
+               /*
+                * Allow the resumed yielding SMC processing to be preempted by
+                * Non-secure interrupts.
+                */
+               ehf_allow_ns_preemption();
+#endif
 
                /* We just need to return to the preempted point in
                 * TSP and the execution will resume as normal.