[PATCH v2 2/2] target/arm: SCR_EL3.RW is RAO/WI without AArch32 EL[12]

[Richard Henderson <richard.henderson@linaro.org>]

Since DDI0487F.a, the RW bit is RAO/WI.  When specifically
targeting such a cpu, e.g. cortex-a76, it is legitimate to
ignore the bit within the secure monitor.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1062
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 target/arm/cpu.h    | 5 +++++
 target/arm/helper.c | 4 ++++
 2 files changed, 9 insertions(+)

diff --git a/target/arm/cpu.h b/target/arm/cpu.h
index 78dbcb5592..c489519923 100644
--- a/target/arm/cpu.h
+++ b/target/arm/cpu.h
@@ -3978,6 +3978,11 @@ static inline bool isar_feature_aa64_aa32_el1(const ARMISARegisters *id)
     return FIELD_EX64(id->id_aa64pfr0, ID_AA64PFR0, EL1) >= 2;
 }
 
+static inline bool isar_feature_aa64_aa32_el2(const ARMISARegisters *id)
+{
+    return FIELD_EX64(id->id_aa64pfr0, ID_AA64PFR0, EL2) >= 2;
+}
+
 static inline bool isar_feature_aa64_ras(const ARMISARegisters *id)
 {
     return FIELD_EX64(id->id_aa64pfr0, ID_AA64PFR0, RAS) != 0;
diff --git a/target/arm/helper.c b/target/arm/helper.c
index d6818f281a..0d1670f89b 100644
--- a/target/arm/helper.c
+++ b/target/arm/helper.c
@@ -1747,6 +1747,10 @@ static void scr_write(CPUARMState *env, const ARMCPRegInfo *ri, uint64_t value)
         value |= SCR_FW | SCR_AW;      /* RES1 */
         valid_mask &= ~SCR_NET;        /* RES0 */
 
+        if (!cpu_isar_feature(aa64_aa32_el1, cpu) &&
+            !cpu_isar_feature(aa64_aa32_el2, cpu)) {
+            value |= SCR_RW;           /* RAO/WI*/
+        }
         if (cpu_isar_feature(aa64_ras, cpu)) {
             valid_mask |= SCR_TERR;
         }
-- 
2.34.1