target/riscv: Implement Ssdbltrp sret, mret and mnret behavior

When the Ssdbltrp extension is enabled, SSTATUS.SDT field is cleared
when executing sret. When executing mret/mnret, SSTATUS.SDT is cleared
when returning to U, VS or VU and VSSTATUS.SDT is cleared when returning
to VU from HS.

Signed-off-by: Clément Léger <cleger@rivosinc.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20250110125441.3208676-4-cleger@rivosinc.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

1 files changed, 34 insertions, 1 deletions

diff --git a/target/riscv/op_helper.c b/target/riscv/op_helper.c
index c825336..59c4bf2 100644
--- a/target/riscv/op_helper.c
+++ b/target/riscv/op_helper.c
@@ -294,6 +294,18 @@ target_ulong helper_sret(CPURISCVState *env)
                         get_field(mstatus, MSTATUS_SPIE));
     mstatus = set_field(mstatus, MSTATUS_SPIE, 1);
     mstatus = set_field(mstatus, MSTATUS_SPP, PRV_U);
+
+    if (riscv_cpu_cfg(env)->ext_ssdbltrp) {
+        if (riscv_has_ext(env, RVH)) {
+            target_ulong prev_vu = get_field(env->hstatus, HSTATUS_SPV) &&
+                                   prev_priv == PRV_U;
+            /* Returning to VU from HS, vsstatus.sdt = 0 */
+            if (!env->virt_enabled && prev_vu) {
+                env->vsstatus = set_field(env->vsstatus, MSTATUS_SDT, 0);
+            }
+        }
+        mstatus = set_field(mstatus, MSTATUS_SDT, 0);
+    }
     if (env->priv_ver >= PRIV_VERSION_1_12_0) {
         mstatus = set_field(mstatus, MSTATUS_MPRV, 0);
     }
@@ -304,7 +316,6 @@ target_ulong helper_sret(CPURISCVState *env)
         target_ulong hstatus = env->hstatus;
 
         prev_virt = get_field(hstatus, HSTATUS_SPV);
-
         hstatus = set_field(hstatus, HSTATUS_SPV, 0);
 
         env->hstatus = hstatus;
@@ -344,6 +355,22 @@ static void check_ret_from_m_mode(CPURISCVState *env, target_ulong retpc,
         riscv_raise_exception(env, RISCV_EXCP_INST_ACCESS_FAULT, GETPC());
     }
 }
+static target_ulong ssdbltrp_mxret(CPURISCVState *env, target_ulong mstatus,
+                                   target_ulong prev_priv,
+                                   target_ulong prev_virt)
+{
+    /* If returning to U, VS or VU, sstatus.sdt = 0 */
+    if (prev_priv == PRV_U || (prev_virt &&
+        (prev_priv == PRV_S || prev_priv == PRV_U))) {
+        mstatus = set_field(mstatus, MSTATUS_SDT, 0);
+        /* If returning to VU, vsstatus.sdt = 0 */
+        if (prev_virt && prev_priv == PRV_U) {
+            env->vsstatus = set_field(env->vsstatus, MSTATUS_SDT, 0);
+        }
+    }
+
+    return mstatus;
+}
 
 target_ulong helper_mret(CPURISCVState *env)
 {
@@ -361,6 +388,9 @@ target_ulong helper_mret(CPURISCVState *env)
     mstatus = set_field(mstatus, MSTATUS_MPP,
                         riscv_has_ext(env, RVU) ? PRV_U : PRV_M);
     mstatus = set_field(mstatus, MSTATUS_MPV, 0);
+    if (riscv_cpu_cfg(env)->ext_ssdbltrp) {
+        mstatus = ssdbltrp_mxret(env, mstatus, prev_priv, prev_virt);
+    }
     if ((env->priv_ver >= PRIV_VERSION_1_12_0) && (prev_priv != PRV_M)) {
         mstatus = set_field(mstatus, MSTATUS_MPRV, 0);
     }
@@ -402,6 +432,9 @@ target_ulong helper_mnret(CPURISCVState *env)
     if (prev_priv < PRV_M) {
         env->mstatus = set_field(env->mstatus, MSTATUS_MPRV, false);
     }
+    if (riscv_cpu_cfg(env)->ext_ssdbltrp) {
+        env->mstatus = ssdbltrp_mxret(env, env->mstatus, prev_priv, prev_virt);
+    }
 
     if (riscv_has_ext(env, RVH) && prev_virt) {
         riscv_cpu_swap_hypervisor_regs(env);