arch-arm: Secure EL2 checking

This patch adds Armv8.4-SecEL2 checking. Helpers implementing
EL2Enabled, IsSecureEL2Enabled and HaveSecureEL2Ext following
the architecture pseudocode are provided. These are intended
to be used for checking register access permissions.

Change-Id: I3d06d0127cf165c1eeaf3302830742d610cef719
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/23766
Maintainer: Giacomo Travaglini <giacomo.travaglini@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/arch/arm/miscregs_types.hh

@@ -294,14 +294,15 @@ namespace ArmISA
     EndBitUnion(NSACR)
 
     BitUnion32(SCR)
+        Bitfield<18> eel2; // AArch64 (Armv8.4-SecEL2)
         Bitfield<13> twe;
         Bitfield<12> twi;
-        Bitfield<11> st;  // AArch64
-        Bitfield<10> rw;  // AArch64
+        Bitfield<11> st;   // AArch64
+        Bitfield<10> rw;   // AArch64
         Bitfield<9> sif;
         Bitfield<8> hce;
         Bitfield<7> scd;
-        Bitfield<7> smd;  // AArch64
+        Bitfield<7> smd;   // AArch64
         Bitfield<6> nEt;
         Bitfield<5> aw;
         Bitfield<4> fw;

src/arch/arm/utility.cc

@@ -289,6 +289,34 @@ getMPIDR(ArmSystem *arm_sys, ThreadContext *tc)
     }
 }
 
+bool
+HaveSecureEL2Ext(ThreadContext *tc)
+{
+    AA64PFR0 id_aa64pfr0 = tc->readMiscReg(MISCREG_ID_AA64PFR0_EL1);
+    return id_aa64pfr0.sel2;
+}
+
+bool
+IsSecureEL2Enabled(ThreadContext *tc)
+{
+    SCR scr = tc->readMiscReg(MISCREG_SCR_EL3);
+    if (ArmSystem::haveEL(tc, EL2) && HaveSecureEL2Ext(tc)) {
+        if (ArmSystem::haveEL(tc, EL3))
+            return !ELIs32(tc, EL3) && scr.eel2;
+        else
+            return inSecureState(tc);
+    }
+    return false;
+}
+
+bool
+EL2Enabled(ThreadContext *tc)
+{
+    SCR scr = tc->readMiscReg(MISCREG_SCR_EL3);
+    return ArmSystem::haveEL(tc, EL2) &&
+           (!ArmSystem::haveEL(tc, EL3) || scr.ns || IsSecureEL2Enabled(tc));
+}
+
 bool
 ELIs64(ThreadContext *tc, ExceptionLevel el)
 {

src/arch/arm/utility.hh

@@ -166,6 +166,10 @@ currEL(CPSR cpsr)
     return opModeToEL((OperatingMode) (uint8_t)cpsr.mode);
 }
 
+bool HaveSecureEL2Ext(ThreadContext *tc);
+bool IsSecureEL2Enabled(ThreadContext *tc);
+bool EL2Enabled(ThreadContext *tc);
+
 /**
  * This function checks whether selected EL provided as an argument
  * is using the AArch32 ISA. This information might be unavailable