target/arm: Handle banking in negative-execution-priority check in cpu_mmu_index()

Now that we have a banked FAULTMASK register and banked exceptions,
we can implement the correct check in cpu_mmu_index() for whether
the MPU_CTRL.HFNMIENA bit's effect should apply. This bit causes
handlers which have requested a negative execution priority to run
with the MPU disabled. In v8M the test has to check this for the
current security state and so takes account of banking.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 1505240046-11454-17-git-send-email-peter.maydell@linaro.org

hw/intc/armv7m_nvic.c

@@ -368,6 +368,35 @@ static inline int nvic_exec_prio(NVICState *s)
     return MIN(running, s->exception_prio);
 }
 
+bool armv7m_nvic_neg_prio_requested(void *opaque, bool secure)
+{
+    /* Return true if the requested execution priority is negative
+     * for the specified security state, ie that security state
+     * has an active NMI or HardFault or has set its FAULTMASK.
+     * Note that this is not the same as whether the execution
+     * priority is actually negative (for instance AIRCR.PRIS may
+     * mean we don't allow FAULTMASK_NS to actually make the execution
+     * priority negative). Compare pseudocode IsReqExcPriNeg().
+     */
+    NVICState *s = opaque;
+
+    if (s->cpu->env.v7m.faultmask[secure]) {
+        return true;
+    }
+
+    if (secure ? s->sec_vectors[ARMV7M_EXCP_HARD].active :
+        s->vectors[ARMV7M_EXCP_HARD].active) {
+        return true;
+    }
+
+    if (s->vectors[ARMV7M_EXCP_NMI].active &&
+        exc_targets_secure(s, ARMV7M_EXCP_NMI) == secure) {
+        return true;
+    }
+
+    return false;
+}
+
 bool armv7m_nvic_can_take_pending_exception(void *opaque)
 {
     NVICState *s = opaque;

target/arm/cpu.h

@@ -1498,6 +1498,21 @@ int armv7m_nvic_complete_irq(void *opaque, int irq);
  * (v8M ARM ARM I_PKLD.)
  */
 int armv7m_nvic_raw_execution_priority(void *opaque);
+/**
+ * armv7m_nvic_neg_prio_requested: return true if the requested execution
+ * priority is negative for the specified security state.
+ * @opaque: the NVIC
+ * @secure: the security state to test
+ * This corresponds to the pseudocode IsReqExecPriNeg().
+ */
+#ifndef CONFIG_USER_ONLY
+bool armv7m_nvic_neg_prio_requested(void *opaque, bool secure);
+#else
+static inline bool armv7m_nvic_neg_prio_requested(void *opaque, bool secure)
+{
+    return false;
+}
+#endif
 
 /* Interface for defining coprocessor registers.
  * Registers are defined in tables of arm_cp_reginfo structs
@@ -2283,11 +2298,7 @@ static inline int cpu_mmu_index(CPUARMState *env, bool ifetch)
     if (arm_feature(env, ARM_FEATURE_M)) {
         ARMMMUIdx mmu_idx = el == 0 ? ARMMMUIdx_MUser : ARMMMUIdx_MPriv;
 
-        /* Execution priority is negative if FAULTMASK is set or
+        if (armv7m_nvic_neg_prio_requested(env->nvic, env->v7m.secure)) {
-         * we're in a HardFault or NMI handler.
-         */
-        if ((env->v7m.exception > 0 && env->v7m.exception <= 3)
-            || env->v7m.faultmask[env->v7m.secure]) {
             mmu_idx = ARMMMUIdx_MNegPri;
         }