target/arm: Fix MTE access checks for disabled SEL2

While not mentioned anywhere in the actual specification text, the
HCR_EL2.ATA bit is treated as '1' when EL2 is disabled at the current
security state. This can be observed in the psuedo-code implementation
of AArch64.AllocationTagAccessIsEnabled().

Signed-off-by: Idan Horowitz <idan.horowitz@gmail.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20220328173107.311267-1-idan.horowitz@gmail.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

target/arm/helper.c

@@ -7176,7 +7176,7 @@ static CPAccessResult access_mte(CPUARMState *env, const ARMCPRegInfo *ri,
 {
     int el = arm_current_el(env);
 
-    if (el < 2 && arm_feature(env, ARM_FEATURE_EL2)) {
+    if (el < 2 && arm_is_el2_enabled(env)) {
         uint64_t hcr = arm_hcr_el2_eff(env);
         if (!(hcr & HCR_ATA) && (!(hcr & HCR_E2H) || !(hcr & HCR_TGE))) {
             return CP_ACCESS_TRAP_EL2;

target/arm/internals.h

@@ -1094,7 +1094,7 @@ static inline bool allocation_tag_access_enabled(CPUARMState *env, int el,
         && !(env->cp15.scr_el3 & SCR_ATA)) {
         return false;
     }
-    if (el < 2 && arm_feature(env, ARM_FEATURE_EL2)) {
+    if (el < 2 && arm_is_el2_enabled(env)) {
         uint64_t hcr = arm_hcr_el2_eff(env);
         if (!(hcr & HCR_ATA) && (!(hcr & HCR_E2H) || !(hcr & HCR_TGE))) {
             return false;