Re: [PATCH v2] target/riscv: Add a property to set vill bit on reserved usage of vsetvli instruction

[Daniel Henrique Barboza]

On 6/18/25 6:35 PM, Vasilis Liaskovitis wrote:

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 <vliaskovi...@suse.com>
---

Reviewed-by: Daniel Henrique Barboza <dbarb...@ventanamicro.com>

  target/riscv/cpu.c                      |  1 +
  target/riscv/cpu_cfg_fields.h.inc       |  1 +
  target/riscv/helper.h                   |  2 +-
  target/riscv/insn_trans/trans_rvv.c.inc |  4 ++--
  target/riscv/vector_helper.c            | 12 +++++++++++-
  5 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
index 629ac37501..1c29ed3b2b 100644
--- a/target/riscv/cpu.c
+++ b/target/riscv/cpu.c
@@ -2595,6 +2595,7 @@ 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 59f134a419..9c78a797cf 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 85d73e492d..f712b1c368 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 2b6077ac06..87071c5d62 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 5dc1c10012..b41c29da0b 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;