target/riscv: Add CTR sctrclr instruction.

CTR extension adds a new instruction sctrclr to quickly
clear the recorded entries buffer.

Signed-off-by: Rajnesh Kanwal <rkanwal@rivosinc.com>
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20250205-b4-ctr_upstream_v6-v6-5-439d8e06c8ef@rivosinc.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

target/riscv/cpu.h

@@ -619,6 +619,7 @@ void riscv_cpu_set_mode(CPURISCVState *env, target_ulong newpriv, bool virt_en);
 
 void riscv_ctr_add_entry(CPURISCVState *env, target_long src, target_long dst,
     enum CTRType type, target_ulong prev_priv, bool prev_virt);
+void riscv_ctr_clear(CPURISCVState *env);
 
 void riscv_translate_init(void);
 void riscv_translate_code(CPUState *cs, TranslationBlock *tb,

target/riscv/cpu_helper.c

@@ -887,6 +887,13 @@ static void riscv_ctr_freeze(CPURISCVState *env, uint64_t freeze_mask,
     }
 }
 
+void riscv_ctr_clear(CPURISCVState *env)
+{
+    memset(env->ctr_src, 0x0, sizeof(env->ctr_src));
+    memset(env->ctr_dst, 0x0, sizeof(env->ctr_dst));
+    memset(env->ctr_data, 0x0, sizeof(env->ctr_data));
+}
+
 static uint64_t riscv_ctr_priv_to_mask(target_ulong priv, bool virt)
 {
     switch (priv) {

target/riscv/helper.h

@@ -132,6 +132,7 @@ DEF_HELPER_6(csrrw_i128, tl, env, int, tl, tl, tl, tl)
 DEF_HELPER_1(sret, tl, env)
 DEF_HELPER_1(mret, tl, env)
 DEF_HELPER_1(mnret, tl, env)
+DEF_HELPER_1(ctr_clear, void, env)
 DEF_HELPER_1(wfi, void, env)
 DEF_HELPER_1(wrs_nto, void, env)
 DEF_HELPER_1(tlb_flush, void, env)

target/riscv/insn32.decode

@@ -114,6 +114,7 @@
 # *** Privileged Instructions ***
 ecall       000000000000     00000 000 00000 1110011
 ebreak      000000000001     00000 000 00000 1110011
+sctrclr     000100000100     00000 000 00000 1110011
 uret        0000000    00010 00000 000 00000 1110011
 sret        0001000    00010 00000 000 00000 1110011
 mret        0011000    00010 00000 000 00000 1110011

target/riscv/insn_trans/trans_privileged.c.inc

@@ -75,6 +75,17 @@ static bool trans_ebreak(DisasContext *ctx, arg_ebreak *a)
     return true;
 }
 
+static bool trans_sctrclr(DisasContext *ctx, arg_sctrclr *a)
+{
+#ifndef CONFIG_USER_ONLY
+    if (ctx->cfg_ptr->ext_smctr || ctx->cfg_ptr->ext_ssctr) {
+        gen_helper_ctr_clear(tcg_env);
+        return true;
+    }
+#endif
+    return false;
+}
+
 static bool trans_uret(DisasContext *ctx, arg_uret *a)
 {
     return false;

target/riscv/op_helper.c

@@ -485,6 +485,35 @@ void helper_ctr_add_entry(CPURISCVState *env, target_ulong src,
                         env->priv, env->virt_enabled);
 }
 
+void helper_ctr_clear(CPURISCVState *env)
+{
+    /*
+     * It's safe to call smstateen_acc_ok() for umode access regardless of the
+     * state of bit 54 (CTR bit in case of m/hstateen) of sstateen. If the bit
+     * is zero, smstateen_acc_ok() will return the correct exception code and
+     * if it's one, smstateen_acc_ok() will return RISCV_EXCP_NONE. In that
+     * scenario the U-mode check below will handle that case.
+     */
+    RISCVException ret = smstateen_acc_ok(env, 0, SMSTATEEN0_CTR);
+    if (ret != RISCV_EXCP_NONE) {
+        riscv_raise_exception(env, ret, GETPC());
+    }
+
+    if (env->priv == PRV_U) {
+        /*
+         * One corner case is when sctrclr is executed from VU-mode and
+         * mstateen.CTR = 0, in which case we are supposed to raise
+         * RISCV_EXCP_ILLEGAL_INST. This case is already handled in
+         * smstateen_acc_ok().
+         */
+        uint32_t excep = env->virt_enabled ? RISCV_EXCP_VIRT_INSTRUCTION_FAULT :
+            RISCV_EXCP_ILLEGAL_INST;
+        riscv_raise_exception(env, excep, GETPC());
+    }
+
+    riscv_ctr_clear(env);
+}
+
 void helper_wfi(CPURISCVState *env)
 {
     CPUState *cs = env_cpu(env);