Implement MSTATUS.MDT behavior.

Signed-off-by: Clément Léger <cleger@rivosinc.com>
---
 target/riscv/cpu_bits.h |  1 +
 target/riscv/csr.c      | 15 +++++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/target/riscv/cpu_bits.h b/target/riscv/cpu_bits.h
index 5557a86348..62bab1bf55 100644
--- a/target/riscv/cpu_bits.h
+++ b/target/riscv/cpu_bits.h
@@ -561,6 +561,7 @@
 #define MSTATUS_SDT         0x01000000
 #define MSTATUS_GVA         0x4000000000ULL
 #define MSTATUS_MPV         0x8000000000ULL
+#define MSTATUS_MDT         0x40000000000ULL /* Smdbltrp extension */
 
 #define MSTATUS64_UXL       0x0000000300000000ULL
 #define MSTATUS64_SXL       0x0000000C00000000ULL
diff --git a/target/riscv/csr.c b/target/riscv/csr.c
index d8280ec956..cc1940447a 100644
--- a/target/riscv/csr.c
+++ b/target/riscv/csr.c
@@ -1617,6 +1617,14 @@ static RISCVException write_mstatus(CPURISCVState *env, int csrno,
         }
     }
 
+    if (riscv_cpu_cfg(env)->ext_smdbltrp) {
+        mask |= MSTATUS_MDT;
+        if ((val & MSTATUS_MDT) != 0) {
+            mstatus &= ~MSTATUS_MIE;
+            val &= ~MSTATUS_MIE;
+        }
+    }
+
     if (xl != MXL_RV32 || env->debugger) {
         if (riscv_has_ext(env, RVH)) {
             mask |= MSTATUS_MPV | MSTATUS_GVA;
@@ -1655,6 +1663,13 @@ static RISCVException write_mstatush(CPURISCVState *env, int csrno,
     uint64_t valh = (uint64_t)val << 32;
     uint64_t mask = riscv_has_ext(env, RVH) ? MSTATUS_MPV | MSTATUS_GVA : 0;
 
+    if (riscv_cpu_cfg(env)->ext_smdbltrp) {
+        mask |= MSTATUS_MDT;
+        if ((val & MSTATUS_MDT) != 0) {
+            env->mstatus &= ~MSTATUS_MIE;
+            val &= ~MSTATUS_MIE;
+        }
+    }
     env->mstatus = (env->mstatus & ~mask) | (valh & mask);
 
     return RISCV_EXCP_NONE;
-- 
2.45.2