target/arm: Implement ARMv8.2-TTS2UXN

The ARMv8.2-TTS2UXN feature extends the XN field in stage 2
translation table descriptors from just bit [54] to bits [54:53],
allowing stage 2 to control execution permissions separately for EL0
and EL1. Implement the new semantics of the XN field and enable
the feature for our 'max' CPU.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20200330210400.11724-5-peter.maydell@linaro.org

target/arm/cpu.c

@@ -2686,6 +2686,7 @@ static void arm_max_initfn(Object *obj)
             t = FIELD_DP32(t, ID_MMFR4, HPDS, 1); /* AA32HPD */
             t = FIELD_DP32(t, ID_MMFR4, AC2, 1); /* ACTLR2, HACTLR2 */
             t = FIELD_DP32(t, ID_MMFR4, CNP, 1); /* TTCNP */
+            t = FIELD_DP32(t, ID_MMFR4, XNX, 1); /* TTS2UXN */
             cpu->isar.id_mmfr4 = t;
         }
 #endif

target/arm/cpu.h

@@ -3610,6 +3610,11 @@ static inline bool isar_feature_aa32_ccidx(const ARMISARegisters *id)
     return FIELD_EX32(id->id_mmfr4, ID_MMFR4, CCIDX) != 0;
 }
 
+static inline bool isar_feature_aa32_tts2uxn(const ARMISARegisters *id)
+{
+    return FIELD_EX32(id->id_mmfr4, ID_MMFR4, XNX) != 0;
+}
+
 /*
  * 64-bit feature tests via id registers.
  */
@@ -3822,6 +3827,11 @@ static inline bool isar_feature_aa64_ccidx(const ARMISARegisters *id)
     return FIELD_EX64(id->id_aa64mmfr2, ID_AA64MMFR2, CCIDX) != 0;
 }
 
+static inline bool isar_feature_aa64_tts2uxn(const ARMISARegisters *id)
+{
+    return FIELD_EX64(id->id_aa64mmfr1, ID_AA64MMFR1, XNX) != 0;
+}
+
 /*
  * Feature tests for "does this exist in either 32-bit or 64-bit?"
  */
@@ -3850,6 +3860,11 @@ static inline bool isar_feature_any_ccidx(const ARMISARegisters *id)
     return isar_feature_aa64_ccidx(id) || isar_feature_aa32_ccidx(id);
 }
 
+static inline bool isar_feature_any_tts2uxn(const ARMISARegisters *id)
+{
+    return isar_feature_aa64_tts2uxn(id) || isar_feature_aa32_tts2uxn(id);
+}
+
 /*
  * Forward to the above feature tests given an ARMCPU pointer.
  */

target/arm/cpu64.c

@@ -673,6 +673,7 @@ static void aarch64_max_initfn(Object *obj)
         t = FIELD_DP64(t, ID_AA64MMFR1, VH, 1);
         t = FIELD_DP64(t, ID_AA64MMFR1, PAN, 2); /* ATS1E1 */
         t = FIELD_DP64(t, ID_AA64MMFR1, VMIDBITS, 2); /* VMID16 */
+        t = FIELD_DP64(t, ID_AA64MMFR1, XNX, 1); /* TTS2UXN */
         cpu->isar.id_aa64mmfr1 = t;
 
         t = cpu->isar.id_aa64mmfr2;
@@ -706,6 +707,7 @@ static void aarch64_max_initfn(Object *obj)
         u = FIELD_DP32(u, ID_MMFR4, HPDS, 1); /* AA32HPD */
         u = FIELD_DP32(u, ID_MMFR4, AC2, 1); /* ACTLR2, HACTLR2 */
         u = FIELD_DP32(u, ID_MMFR4, CNP, 1); /* TTCNP */
+        u = FIELD_DP32(u, ID_MMFR4, XNX, 1); /* TTS2UXN */
         cpu->isar.id_mmfr4 = u;
 
         u = cpu->isar.id_aa64dfr0;

target/arm/helper.c

@@ -9908,9 +9908,10 @@ simple_ap_to_rw_prot(CPUARMState *env, ARMMMUIdx mmu_idx, int ap)
  *
  * @env:     CPUARMState
  * @s2ap:    The 2-bit stage2 access permissions (S2AP)
- * @xn:      XN (execute-never) bit
+ * @xn:      XN (execute-never) bits
+ * @s1_is_el0: true if this is S2 of an S1+2 walk for EL0
  */
-static int get_S2prot(CPUARMState *env, int s2ap, int xn)
+static int get_S2prot(CPUARMState *env, int s2ap, int xn, bool s1_is_el0)
 {
     int prot = 0;
 
@@ -9920,9 +9921,32 @@ static int get_S2prot(CPUARMState *env, int s2ap, int xn)
     if (s2ap & 2) {
         prot |= PAGE_WRITE;
     }
-    if (!xn) {
+
-        if (arm_el_is_aa64(env, 2) || prot & PAGE_READ) {
+    if (cpu_isar_feature(any_tts2uxn, env_archcpu(env))) {
+        switch (xn) {
+        case 0:
             prot |= PAGE_EXEC;
+            break;
+        case 1:
+            if (s1_is_el0) {
+                prot |= PAGE_EXEC;
+            }
+            break;
+        case 2:
+            break;
+        case 3:
+            if (!s1_is_el0) {
+                prot |= PAGE_EXEC;
+            }
+            break;
+        default:
+            g_assert_not_reached();
+        }
+    } else {
+        if (!extract32(xn, 1, 1)) {
+            if (arm_el_is_aa64(env, 2) || prot & PAGE_READ) {
+                prot |= PAGE_EXEC;
+            }
         }
     }
     return prot;
@@ -10901,13 +10925,14 @@ static bool get_phys_addr_lpae(CPUARMState *env, target_ulong address,
     }
 
     ap = extract32(attrs, 4, 2);
-    xn = extract32(attrs, 12, 1);
 
     if (mmu_idx == ARMMMUIdx_Stage2) {
         ns = true;
-        *prot = get_S2prot(env, ap, xn);
+        xn = extract32(attrs, 11, 2);
+        *prot = get_S2prot(env, ap, xn, s1_is_el0);
     } else {
         ns = extract32(attrs, 3, 1);
+        xn = extract32(attrs, 12, 1);
         pxn = extract32(attrs, 11, 1);
         *prot = get_S1prot(env, mmu_idx, aarch64, ap, ns, xn, pxn);
     }