[PATCH for-6.1 6/6] hw/intc/armv7m_nvic: for v8.1M VECTPENDING hides S exceptions from NS

[Peter Maydell <peter.maydell@linaro.org>]

In Arm v8.1M the VECTPENDING field in the ICSR has new behaviour: if
the register is accessed NonSecure and the highest priority pending
enabled exception (that would be returned in the VECTPENDING field)
targets Secure, then the VECTPENDING field must read 1 rather than
the exception number of the pending exception. Implement this.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 hw/intc/armv7m_nvic.c | 31 ++++++++++++++++++++++++-------
 1 file changed, 24 insertions(+), 7 deletions(-)

diff --git a/hw/intc/armv7m_nvic.c b/hw/intc/armv7m_nvic.c
index c9149a3b221..1e7ddcb94cb 100644
--- a/hw/intc/armv7m_nvic.c
+++ b/hw/intc/armv7m_nvic.c
@@ -804,6 +804,16 @@ void armv7m_nvic_acknowledge_irq(void *opaque)
     nvic_irq_update(s);
 }
 
+static bool vectpending_targets_secure(NVICState *s)
+{
+    /* Return true if s->vectpending targets Secure state */
+    if (s->vectpending_is_s_banked) {
+        return true;
+    }
+    return !exc_is_banked(s->vectpending) &&
+        exc_targets_secure(s, s->vectpending);
+}
+
 void armv7m_nvic_get_pending_irq_info(void *opaque,
                                       int *pirq, bool *ptargets_secure)
 {
@@ -813,12 +823,7 @@ void armv7m_nvic_get_pending_irq_info(void *opaque,
 
     assert(pending > ARMV7M_EXCP_RESET && pending < s->num_irq);
 
-    if (s->vectpending_is_s_banked) {
-        targets_secure = true;
-    } else {
-        targets_secure = !exc_is_banked(pending) &&
-            exc_targets_secure(s, pending);
-    }
+    targets_secure = vectpending_targets_secure(s);
 
     trace_nvic_get_pending_irq_info(pending, targets_secure);
 
@@ -1039,7 +1044,19 @@ static uint32_t nvic_readl(NVICState *s, uint32_t offset, MemTxAttrs attrs)
         /* VECTACTIVE */
         val = cpu->env.v7m.exception;
         /* VECTPENDING */
-        val |= (s->vectpending & 0x1ff) << 12;
+        if (s->vectpending) {
+            /*
+             * From v8.1M VECTPENDING must read as 1 if accessed as
+             * NonSecure and the highest priority pending and enabled
+             * exception targets Secure.
+             */
+            int vp = s->vectpending;
+            if (!attrs.secure && arm_feature(&cpu->env, ARM_FEATURE_V8_1M) &&
+                vectpending_targets_secure(s)) {
+                vp = 1;
+            }
+            val |= (vp & 0x1ff) << 12;
+        }
         /* ISRPENDING - set if any external IRQ is pending */
         if (nvic_isrpending(s)) {
             val |= (1 << 22);
-- 
2.20.1