[Qemu-devel] [PATCH v2 1/6] target-arm: correct CNTFRQ access rights

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

Correct some corner cases we were getting wrong for
CNTFRQ access rights:
 * should UNDEF from 32-bit Secure EL1
 * only writable from the highest implemented exception level,
   which might not be EL1 now

To clarify the code, provide a new utility function
arm_highest_el() which returns the highest implemented
exception level.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
Rewritten to use arm_highest_el() to improve clarity
---
 target-arm/cpu.h    | 12 ++++++++++++
 target-arm/helper.c | 29 ++++++++++++++++++++++++++---
 2 files changed, 38 insertions(+), 3 deletions(-)

diff --git a/target-arm/cpu.h b/target-arm/cpu.h
index 5137632..afbf366 100644
--- a/target-arm/cpu.h
+++ b/target-arm/cpu.h
@@ -1255,6 +1255,18 @@ static inline bool cptype_valid(int cptype)
 #define PL1_RW (PL1_R | PL1_W)
 #define PL0_RW (PL0_R | PL0_W)
 
+/* Return the highest implemented Exception Level */
+static inline int arm_highest_el(CPUARMState *env)
+{
+    if (arm_feature(env, ARM_FEATURE_EL3)) {
+        return 3;
+    }
+    if (arm_feature(env, ARM_FEATURE_EL2)) {
+        return 2;
+    }
+    return 1;
+}
+
 /* Return the current Exception Level (as per ARMv8; note that this differs
  * from the ARMv7 Privilege Level).
  */
diff --git a/target-arm/helper.c b/target-arm/helper.c
index 2f9db72..4d27c00 100644
--- a/target-arm/helper.c
+++ b/target-arm/helper.c
@@ -1218,10 +1218,33 @@ static const ARMCPRegInfo v6k_cp_reginfo[] = {
 static CPAccessResult gt_cntfrq_access(CPUARMState *env, const ARMCPRegInfo *ri,
                                        bool isread)
 {
-    /* CNTFRQ: not visible from PL0 if both PL0PCTEN and PL0VCTEN are zero */
-    if (arm_current_el(env) == 0 && !extract32(env->cp15.c14_cntkctl, 0, 2)) {
-        return CP_ACCESS_TRAP;
+    /* CNTFRQ: not visible from PL0 if both PL0PCTEN and PL0VCTEN are zero.
+     * Writable only at the highest implemented exception level.
+     */
+    int el = arm_current_el(env);
+
+    switch (el) {
+    case 0:
+        if (!extract32(env->cp15.c14_cntkctl, 0, 2)) {
+            return CP_ACCESS_TRAP;
+        }
+        break;
+    case 1:
+        if (!isread && ri->state == ARM_CP_STATE_AA32 &&
+            arm_is_secure_below_el3(env)) {
+            /* Accesses from 32-bit Secure EL1 UNDEF (*not* trap to EL3!) */
+            return CP_ACCESS_TRAP_UNCATEGORIZED;
+        }
+        break;
+    case 2:
+    case 3:
+        break;
     }
+
+    if (!isread && el < arm_highest_el(env)) {
+        return CP_ACCESS_TRAP_UNCATEGORIZED;
+    }
+
     return CP_ACCESS_OK;
 }
 
-- 
1.9.1