[Qemu-devel] [PATCH v2 9/9] target-arm: Add WFx instruction trap support

[Greg Bellows <greg.bellows@linaro.org>]

Add support for trapping WFI and WFE instructions to the proper EL when
SCTLR/SCR/HCR settings apply.

Signed-off-by: Greg Bellows <greg.bellows@linaro.org>

---

v1 -> v2
- Replace check loop with simpler if checks.
- Changed WFx syncdrome function to take bool
- Changed return of uint32_t to int
- Added cdditional comments.
---
 target-arm/internals.h |  2 +-
 target-arm/op_helper.c | 76 ++++++++++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 74 insertions(+), 4 deletions(-)

diff --git a/target-arm/internals.h b/target-arm/internals.h
index de0a9c1..8e208f7 100644
--- a/target-arm/internals.h
+++ b/target-arm/internals.h
@@ -347,7 +347,7 @@ static inline uint32_t syn_breakpoint(int same_el)
         | ARM_EL_IL | 0x22;
 }
 
-static inline uint32_t syn_wfx(int cv, int cond, int ti)
+static inline uint32_t syn_wfx(int cv, int cond, bool ti)
 {
     return (EC_WFX_TRAP << ARM_EL_EC_SHIFT) |
            (cv << 24) | (cond << 20) | ti;
diff --git a/target-arm/op_helper.c b/target-arm/op_helper.c
index 971edc7..43aa8ef 100644
--- a/target-arm/op_helper.c
+++ b/target-arm/op_helper.c
@@ -223,23 +223,93 @@ uint32_t HELPER(usat16)(CPUARMState *env, uint32_t x, uint32_t shift)
     return res;
 }
 
+/* Function checks whether WFx (WFI/WFE) instructions are set-up to be trapped.
+ * The function returns the target EL (1-3) if the instruction is to be trapped
+ * otherwise it returns 0 indicating it is not trapped.
+ */
+static inline int check_wfx_trap(CPUARMState *env, bool is_wfe)
+{
+    int cur_el = arm_current_el(env);
+    uint64_t mask;
+
+    /* If we are currently in EL0 then we need to check if SCTLR is set up for
+     * WFx instructions being trapped to EL1.
+     */
+    if (cur_el < 1) {
+        mask = is_wfe ? SCTLR_nTWE : SCTLR_nTWI;
+        if (arm_el_is_aa64(env, 1)) {
+            if (!(env->cp15.sctlr_el[1] & mask)) {
+                return 1;
+            }
+        } else if (arm_feature(env, ARM_FEATURE_V8)) {
+            /* SCTLR WFx SCTLR trap bits only exist in ARMv8 */
+            if (!(A32_BANKED_CURRENT_REG_GET(env, sctlr) & mask)) {
+                return 1;
+            }
+        }
+    }
+
+    /* We are not trapping to EL1 at this point.
+     * Check if we are trapping WFx to EL2 it present.
+     */
+    if (cur_el < 2) {
+        if (arm_feature(env, ARM_FEATURE_EL2) && !arm_is_secure(env)) {
+            mask = (is_wfe) ? HCR_TWE : HCR_TWI;
+            if (env->cp15.hcr_el2 & mask) {
+                return 2;
+            }
+        }
+    }
+
+    /* We are not trapping to EL1 or EL2 at this point.
+     * Check if we are trapping WFx to EL3 if present.
+     */
+    if (cur_el < 3) {
+        if (arm_feature(env, ARM_FEATURE_EL3) &&
+            arm_feature(env, ARM_FEATURE_V8)) {
+            mask = (is_wfe) ? SCR_TWE : SCR_TWI;
+            if (env->cp15.scr_el3 & mask) {
+                return 3;
+            }
+        }
+    }
+
+    return 0;
+}
+
 void HELPER(wfi)(CPUARMState *env)
 {
     CPUState *cs = CPU(arm_env_get_cpu(env));
+    int target_el = check_wfx_trap(env, false);
 
-    cs->exception_index = EXCP_HLT;
-    cs->halted = 1;
+    if (target_el) {
+        cs->exception_index = EXCP_UDEF;
+        env->exception.syndrome = syn_wfx(1, 0xe, false);
+        env->exception.target_el = target_el;
+        env->pc -= 4;
+    } else {
+        cs->exception_index = EXCP_HLT;
+        cs->halted = 1;
+    }
     cpu_loop_exit(cs);
 }
 
 void HELPER(wfe)(CPUARMState *env)
 {
     CPUState *cs = CPU(arm_env_get_cpu(env));
+    int target_el = check_wfx_trap(env, true);
 
     /* Don't actually halt the CPU, just yield back to top
      * level loop
      */
-    cs->exception_index = EXCP_YIELD;
+    if (target_el) {
+        cs->exception_index = EXCP_UDEF;
+        env->exception.syndrome = syn_wfx(1, 0xe, true);
+        env->exception.target_el = target_el;
+        env->pc -= 4;
+    } else {
+        cs->exception_index = EXCP_YIELD;
+    }
     cpu_loop_exit(cs);
 }
 
-- 
1.8.3.2