target/arm: honor HCR_E2H and HCR_TGE in arm_excp_unmasked()

An exception targeting EL2 from lower EL is actually maskable when
HCR_E2H and HCR_TGE are both set. This applies to both secure and
non-secure Security state.

We can remove the conditions that try to suppress masking of
interrupts when we are Secure and the exception targets EL2 and
Secure EL2 is disabled.  This is OK because in that situation
arm_phys_excp_target_el() will never return 2 as the target EL.  The
'not if secure' check in this function was originally written before
arm_hcr_el2_eff(), and back then the target EL returned by
arm_phys_excp_target_el() could be 2 even if we were in Secure
EL0/EL1; but it is no longer needed.

Signed-off-by: Ake Koomsin <ake@igel.co.jp>
Message-id: 20221017092432.546881-1-ake@igel.co.jp
[PMM: Add commit message paragraph explaining why it's OK to
 remove the checks on secure and SCR_EEL2]
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

target/arm/cpu.c

@@ -587,14 +587,24 @@ static inline bool arm_excp_unmasked(CPUState *cs, unsigned int excp_idx,
     if ((target_el > cur_el) && (target_el != 1)) {
         /* Exceptions targeting a higher EL may not be maskable */
         if (arm_feature(env, ARM_FEATURE_AARCH64)) {
-            /*
-             * 64-bit masking rules are simple: exceptions to EL3
-             * can't be masked, and exceptions to EL2 can only be
-             * masked from Secure state. The HCR and SCR settings
-             * don't affect the masking logic, only the interrupt routing.
-             */
-            if (target_el == 3 || !secure || (env->cp15.scr_el3 & SCR_EEL2)) {
+            switch (target_el) {
+            case 2:
+                /*
+                 * According to ARM DDI 0487H.a, an interrupt can be masked
+                 * when HCR_E2H and HCR_TGE are both set regardless of the
+                 * current Security state. Note that we need to revisit this
+                 * part again once we need to support NMI.
+                 */
+                if ((hcr_el2 & (HCR_E2H | HCR_TGE)) != (HCR_E2H | HCR_TGE)) {
+                        unmasked = true;
+                }
+                break;
+            case 3:
+                /* Interrupt cannot be masked when the target EL is 3 */
                 unmasked = true;
+                break;
+            default:
+                g_assert_not_reached();
             }
         } else {
             /*