[PATCH v2 2/2] target/riscv: Legalize MPP value in write_mstatus

[Weiwei Li <liweiwei@iscas.ac.cn>]

mstatus.MPP field is a WARL field since priv version 1.11, so we
remain it unchanged if an invalid value is written into it. And
after this, RVH shouldn't be passed to riscv_cpu_set_mode().

Signed-off-by: Weiwei Li <liweiwei@iscas.ac.cn>
Signed-off-by: Junqiang Wang <wangjunqiang@iscas.ac.cn>
---
 target/riscv/cpu_helper.c |  5 +----
 target/riscv/csr.c        | 18 ++++++++++++++++++
 2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
index 2310c7905f..6148f221c3 100644
--- a/target/riscv/cpu_helper.c
+++ b/target/riscv/cpu_helper.c
@@ -647,12 +647,9 @@ void riscv_cpu_set_aia_ireg_rmw_fn(CPURISCVState *env, uint32_t priv,
 
 void riscv_cpu_set_mode(CPURISCVState *env, target_ulong newpriv)
 {
-    if (newpriv > PRV_M) {
+    if (newpriv > PRV_M || newpriv == PRV_H) {
         g_assert_not_reached();
     }
-    if (newpriv == PRV_H) {
-        newpriv = PRV_U;
-    }
     if (icount_enabled() && newpriv != env->priv) {
         riscv_itrigger_update_priv(env);
     }
diff --git a/target/riscv/csr.c b/target/riscv/csr.c
index e0b871f6dc..f3ae726853 100644
--- a/target/riscv/csr.c
+++ b/target/riscv/csr.c
@@ -1230,6 +1230,18 @@ static bool validate_vm(CPURISCVState *env, target_ulong vm)
            satp_mode_max_from_map(riscv_cpu_cfg(env)->satp_mode.map);
 }
 
+static target_ulong legalize_mpp(CPURISCVState *env, target_ulong old_mpp,
+                                 target_ulong val)
+{
+    target_ulong new_mpp = get_field(val, MSTATUS_MPP);
+    bool mpp_invalid = (new_mpp == PRV_S && !riscv_has_ext(env, RVS)) ||
+                       (new_mpp == PRV_U && !riscv_has_ext(env, RVU)) ||
+                       (new_mpp == PRV_H);
+
+    /* Remain field unchanged if new_mpp value is invalid */
+    return mpp_invalid ? set_field(val, MSTATUS_MPP, old_mpp) : val;
+}
+
 static RISCVException write_mstatus(CPURISCVState *env, int csrno,
                                     target_ulong val)
 {
@@ -1237,6 +1249,12 @@ static RISCVException write_mstatus(CPURISCVState *env, int csrno,
     uint64_t mask = 0;
     RISCVMXL xl = riscv_cpu_mxl(env);
 
+    /*
+     * MPP field have been made WARL since priv version 1.11. However,
+     * legalization for it will not break any software running on 1.10.
+     */
+    val = legalize_mpp(env, get_field(mstatus, MSTATUS_MPP), val);
+
     /* flush tlb on mstatus fields that affect VM */
     if ((val ^ mstatus) & (MSTATUS_MXR | MSTATUS_MPP | MSTATUS_MPV |
             MSTATUS_MPRV | MSTATUS_SUM)) {
-- 
2.25.1