nvic: Handle banked exceptions in nvic_recompute_state()

Update the nvic_recompute_state() code to handle the security
extension and its associated banked registers.

Code that uses the resulting cached state (ie the irq
acknowledge and complete code) will be updated in a later
commit.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 1505240046-11454-9-git-send-email-peter.maydell@linaro.org

1 files changed, 146 insertions, 5 deletions

diff --git a/hw/intc/armv7m_nvic.c b/hw/intc/armv7m_nvic.c
index 150c719..7081158 100644
--- a/hw/intc/armv7m_nvic.c
+++ b/hw/intc/armv7m_nvic.c
@@ -54,6 +54,8 @@
  * (higher than the highest possible priority value)
  */
 #define NVIC_NOEXC_PRIO 0x100
+/* Maximum priority of non-secure exceptions when AIRCR.PRIS is set */
+#define NVIC_NS_PRIO_LIMIT 0x80
 
 static const uint8_t nvic_id[] = {
     0x00, 0xb0, 0x1b, 0x00, 0x0d, 0xe0, 0x05, 0xb1
@@ -126,13 +128,139 @@ static bool nvic_isrpending(NVICState *s)
     return false;
 }
 
+static bool exc_is_banked(int exc)
+{
+    /* Return true if this is one of the limited set of exceptions which
+     * are banked (and thus have state in sec_vectors[])
+     */
+    return exc == ARMV7M_EXCP_HARD ||
+        exc == ARMV7M_EXCP_MEM ||
+        exc == ARMV7M_EXCP_USAGE ||
+        exc == ARMV7M_EXCP_SVC ||
+        exc == ARMV7M_EXCP_PENDSV ||
+        exc == ARMV7M_EXCP_SYSTICK;
+}
+
 /* Return a mask word which clears the subpriority bits from
  * a priority value for an M-profile exception, leaving only
  * the group priority.
  */
-static inline uint32_t nvic_gprio_mask(NVICState *s)
+static inline uint32_t nvic_gprio_mask(NVICState *s, bool secure)
+{
+    return ~0U << (s->prigroup[secure] + 1);
+}
+
+static bool exc_targets_secure(NVICState *s, int exc)
+{
+    /* Return true if this non-banked exception targets Secure state. */
+    if (!arm_feature(&s->cpu->env, ARM_FEATURE_M_SECURITY)) {
+        return false;
+    }
+
+    if (exc >= NVIC_FIRST_IRQ) {
+        return !s->itns[exc];
+    }
+
+    /* Function shouldn't be called for banked exceptions. */
+    assert(!exc_is_banked(exc));
+
+    switch (exc) {
+    case ARMV7M_EXCP_NMI:
+    case ARMV7M_EXCP_BUS:
+        return !(s->cpu->env.v7m.aircr & R_V7M_AIRCR_BFHFNMINS_MASK);
+    case ARMV7M_EXCP_SECURE:
+        return true;
+    case ARMV7M_EXCP_DEBUG:
+        /* TODO: controlled by DEMCR.SDME, which we don't yet implement */
+        return false;
+    default:
+        /* reset, and reserved (unused) low exception numbers.
+         * We'll get called by code that loops through all the exception
+         * numbers, but it doesn't matter what we return here as these
+         * non-existent exceptions will never be pended or active.
+         */
+        return true;
+    }
+}
+
+static int exc_group_prio(NVICState *s, int rawprio, bool targets_secure)
+{
+    /* Return the group priority for this exception, given its raw
+     * (group-and-subgroup) priority value and whether it is targeting
+     * secure state or not.
+     */
+    if (rawprio < 0) {
+        return rawprio;
+    }
+    rawprio &= nvic_gprio_mask(s, targets_secure);
+    /* AIRCR.PRIS causes us to squash all NS priorities into the
+     * lower half of the total range
+     */
+    if (!targets_secure &&
+        (s->cpu->env.v7m.aircr & R_V7M_AIRCR_PRIS_MASK)) {
+        rawprio = (rawprio >> 1) + NVIC_NS_PRIO_LIMIT;
+    }
+    return rawprio;
+}
+
+/* Recompute vectpending and exception_prio for a CPU which implements
+ * the Security extension
+ */
+static void nvic_recompute_state_secure(NVICState *s)
 {
-    return ~0U << (s->prigroup[M_REG_NS] + 1);
+    int i, bank;
+    int pend_prio = NVIC_NOEXC_PRIO;
+    int active_prio = NVIC_NOEXC_PRIO;
+    int pend_irq = 0;
+    bool pending_is_s_banked = false;
+
+    /* R_CQRV: precedence is by:
+     *  - lowest group priority; if both the same then
+     *  - lowest subpriority; if both the same then
+     *  - lowest exception number; if both the same (ie banked) then
+     *  - secure exception takes precedence
+     * Compare pseudocode RawExecutionPriority.
+     * Annoyingly, now we have two prigroup values (for S and NS)
+     * we can't do the loop comparison on raw priority values.
+     */
+    for (i = 1; i < s->num_irq; i++) {
+        for (bank = M_REG_S; bank >= M_REG_NS; bank--) {
+            VecInfo *vec;
+            int prio;
+            bool targets_secure;
+
+            if (bank == M_REG_S) {
+                if (!exc_is_banked(i)) {
+                    continue;
+                }
+                vec = &s->sec_vectors[i];
+                targets_secure = true;
+            } else {
+                vec = &s->vectors[i];
+                targets_secure = !exc_is_banked(i) && exc_targets_secure(s, i);
+            }
+
+            prio = exc_group_prio(s, vec->prio, targets_secure);
+            if (vec->enabled && vec->pending && prio < pend_prio) {
+                pend_prio = prio;
+                pend_irq = i;
+                pending_is_s_banked = (bank == M_REG_S);
+            }
+            if (vec->active && prio < active_prio) {
+                active_prio = prio;
+            }
+        }
+    }
+
+    s->vectpending_is_s_banked = pending_is_s_banked;
+    s->vectpending = pend_irq;
+    s->vectpending_prio = pend_prio;
+    s->exception_prio = active_prio;
+
+    trace_nvic_recompute_state_secure(s->vectpending,
+                                      s->vectpending_is_s_banked,
+                                      s->vectpending_prio,
+                                      s->exception_prio);
 }
 
 /* Recompute vectpending and exception_prio */
@@ -143,6 +271,18 @@ static void nvic_recompute_state(NVICState *s)
     int active_prio = NVIC_NOEXC_PRIO;
     int pend_irq = 0;
 
+    /* In theory we could write one function that handled both
+     * the "security extension present" and "not present"; however
+     * the security related changes significantly complicate the
+     * recomputation just by themselves and mixing both cases together
+     * would be even worse, so we retain a separate non-secure-only
+     * version for CPUs which don't implement the security extension.
+     */
+    if (arm_feature(&s->cpu->env, ARM_FEATURE_M_SECURITY)) {
+        nvic_recompute_state_secure(s);
+        return;
+    }
+
     for (i = 1; i < s->num_irq; i++) {
         VecInfo *vec = &s->vectors[i];
 
@@ -156,11 +296,11 @@ static void nvic_recompute_state(NVICState *s)
     }
 
     if (active_prio > 0) {
-        active_prio &= nvic_gprio_mask(s);
+        active_prio &= nvic_gprio_mask(s, false);
     }
 
     if (pend_prio > 0) {
-        pend_prio &= nvic_gprio_mask(s);
+        pend_prio &= nvic_gprio_mask(s, false);
     }
 
     s->vectpending = pend_irq;
@@ -186,7 +326,8 @@ static inline int nvic_exec_prio(NVICState *s)
     } else if (env->v7m.primask[env->v7m.secure]) {
         running = 0;
     } else if (env->v7m.basepri[env->v7m.secure] > 0) {
-        running = env->v7m.basepri[env->v7m.secure] & nvic_gprio_mask(s);
+        running = env->v7m.basepri[env->v7m.secure] &
+            nvic_gprio_mask(s, env->v7m.secure);
     } else {
         running = NVIC_NOEXC_PRIO; /* lower than any possible priority */
     }