target/riscv: Add a property to set vill bit on reserved usage of vsetvli instruction

Usage of vsetvli instruction is reserved if VLMAX is changed when vsetvli rs1
and rd arguments are x0.

In this case, if the new property is true, only the vill bit will be set.

See https://github.com/riscv/riscv-isa-manual/blob/main/src/v-st-ext.adoc#avl-encoding
According to the spec, the above use cases are reserved, and
"Implementations may set vill in either case."

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2422
Signed-off-by: Vasilis Liaskovitis <vliaskovitis@suse.com>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Message-ID: <20250618213542.22873-1-vliaskovitis@suse.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

5 files changed, 16 insertions, 4 deletions

diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
index e3f8ece..6f1d061 100644
--- a/target/riscv/cpu.c
+++ b/target/riscv/cpu.c
@@ -2632,6 +2632,7 @@ static const Property riscv_cpu_properties[] = {
     DEFINE_PROP_BOOL("rvv_ta_all_1s", RISCVCPU, cfg.rvv_ta_all_1s, false),
     DEFINE_PROP_BOOL("rvv_ma_all_1s", RISCVCPU, cfg.rvv_ma_all_1s, false),
     DEFINE_PROP_BOOL("rvv_vl_half_avl", RISCVCPU, cfg.rvv_vl_half_avl, false),
+    DEFINE_PROP_BOOL("rvv_vsetvl_x0_vill", RISCVCPU, cfg.rvv_vsetvl_x0_vill, false),
 
     /*
      * write_misa() is marked as experimental for now so mark
diff --git a/target/riscv/cpu_cfg_fields.h.inc b/target/riscv/cpu_cfg_fields.h.inc
index 33c4f9b..98ceb7b 100644
--- a/target/riscv/cpu_cfg_fields.h.inc
+++ b/target/riscv/cpu_cfg_fields.h.inc
@@ -114,6 +114,7 @@ BOOL_FIELD(ext_supm)
 BOOL_FIELD(rvv_ta_all_1s)
 BOOL_FIELD(rvv_ma_all_1s)
 BOOL_FIELD(rvv_vl_half_avl)
+BOOL_FIELD(rvv_vsetvl_x0_vill)
 /* Named features  */
 BOOL_FIELD(ext_svade)
 BOOL_FIELD(ext_zic64b)
diff --git a/target/riscv/helper.h b/target/riscv/helper.h
index 85d73e4..f712b1c 100644
--- a/target/riscv/helper.h
+++ b/target/riscv/helper.h
@@ -159,7 +159,7 @@ DEF_HELPER_FLAGS_3(hyp_hsv_d, TCG_CALL_NO_WG, void, env, tl, tl)
 #endif
 
 /* Vector functions */
-DEF_HELPER_3(vsetvl, tl, env, tl, tl)
+DEF_HELPER_4(vsetvl, tl, env, tl, tl, tl)
 DEF_HELPER_5(vle8_v, void, ptr, ptr, tl, env, i32)
 DEF_HELPER_5(vle16_v, void, ptr, ptr, tl, env, i32)
 DEF_HELPER_5(vle32_v, void, ptr, ptr, tl, env, i32)
diff --git a/target/riscv/insn_trans/trans_rvv.c.inc b/target/riscv/insn_trans/trans_rvv.c.inc
index 4cd030c..610bf9f 100644
--- a/target/riscv/insn_trans/trans_rvv.c.inc
+++ b/target/riscv/insn_trans/trans_rvv.c.inc
@@ -202,7 +202,7 @@ static bool do_vsetvl(DisasContext *s, int rd, int rs1, TCGv s2)
         s1 = get_gpr(s, rs1, EXT_ZERO);
     }
 
-    gen_helper_vsetvl(dst, tcg_env, s1, s2);
+    gen_helper_vsetvl(dst, tcg_env, s1, s2, tcg_constant_tl((int) (rd == 0 && rs1 == 0)));
     gen_set_gpr(s, rd, dst);
     finalize_rvv_inst(s);
 
@@ -222,7 +222,7 @@ static bool do_vsetivli(DisasContext *s, int rd, TCGv s1, TCGv s2)
 
     dst = dest_gpr(s, rd);
 
-    gen_helper_vsetvl(dst, tcg_env, s1, s2);
+    gen_helper_vsetvl(dst, tcg_env, s1, s2, tcg_constant_tl(0));
     gen_set_gpr(s, rd, dst);
     finalize_rvv_inst(s);
     gen_update_pc(s, s->cur_insn_len);
diff --git a/target/riscv/vector_helper.c b/target/riscv/vector_helper.c
index 5dc1c10..b41c29d 100644
--- a/target/riscv/vector_helper.c
+++ b/target/riscv/vector_helper.c
@@ -35,7 +35,7 @@
 #include <math.h>
 
 target_ulong HELPER(vsetvl)(CPURISCVState *env, target_ulong s1,
-                            target_ulong s2)
+                            target_ulong s2, target_ulong x0)
 {
     int vlmax, vl;
     RISCVCPU *cpu = env_archcpu(env);
@@ -83,6 +83,16 @@ target_ulong HELPER(vsetvl)(CPURISCVState *env, target_ulong s1,
     } else {
         vl = vlmax;
     }
+
+    if (cpu->cfg.rvv_vsetvl_x0_vill && x0 && (env->vl != vl)) {
+        /* only set vill bit. */
+        env->vill = 1;
+        env->vtype = 0;
+        env->vl = 0;
+        env->vstart = 0;
+        return 0;
+    }
+
     env->vl = vl;
     env->vtype = s2;
     env->vstart = 0;