VSTIP is only writable when both [mh]envcfg.STCE is enabled, or it will
revert it's defined behavior as if sstc extension is not implemented.

Signed-off-by: Jim Shu <jim.shu@sifive.com>
---
 target/riscv/csr.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/target/riscv/csr.c b/target/riscv/csr.c
index 49566d3c08..ba026dfc8e 100644
--- a/target/riscv/csr.c
+++ b/target/riscv/csr.c
@@ -3630,7 +3630,14 @@ static RISCVException rmw_mip64(CPURISCVState *env, int csrno,
     if (riscv_cpu_cfg(env)->ext_sstc && (env->priv == PRV_M) &&
         get_field(env->menvcfg, MENVCFG_STCE)) {
         /* sstc extension forbids STIP & VSTIP to be writeable in mip */
-        mask = mask & ~(MIP_STIP | MIP_VSTIP);
+
+        /* STIP is not writable when menvcfg.STCE is enabled. */
+        mask = mask & ~MIP_STIP;
+
+        /* VSTIP is not writable when both [mh]envcfg.STCE are enabled. */
+        if (get_field(env->henvcfg, HENVCFG_STCE)) {
+            mask = mask & ~MIP_VSTIP;
+        }
     }
 
     if (mask) {
-- 
2.17.1