target/riscv: Add counter delegation/configuration support

The Smcdeleg/Ssccfg adds the support for counter delegation via
S*indcsr and Ssccfg.

It also adds a new shadow CSR scountinhibit and menvcfg enable bit (CDE)
to enable this extension and scountovf virtualization.

Signed-off-by: Kaiwen Xue <kaiwenx@rivosinc.com>
Co-developed-by: Atish Patra <atishp@rivosinc.com>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Atish Patra <atishp@rivosinc.com>
Message-ID: <20250110-counter_delegation-v5-8-e83d797ae294@rivosinc.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

target/riscv/csr.c

@@ -383,6 +383,21 @@ static RISCVException aia_smode32(CPURISCVState *env, int csrno)
     return smode32(env, csrno);
 }
 
+static RISCVException scountinhibit_pred(CPURISCVState *env, int csrno)
+{
+    RISCVCPU *cpu = env_archcpu(env);
+
+    if (!cpu->cfg.ext_ssccfg || !cpu->cfg.ext_smcdeleg) {
+        return RISCV_EXCP_ILLEGAL_INST;
+    }
+
+    if (env->virt_enabled) {
+        return RISCV_EXCP_VIRT_INSTRUCTION_FAULT;
+    }
+
+    return smode(env, csrno);
+}
+
 static bool csrind_extensions_present(CPURISCVState *env)
 {
     return riscv_cpu_cfg(env)->ext_smcsrind || riscv_cpu_cfg(env)->ext_sscsrind;
@@ -1224,10 +1239,9 @@ done:
     return result;
 }
 
-static RISCVException write_mhpmcounter(CPURISCVState *env, int csrno,
+static RISCVException riscv_pmu_write_ctr(CPURISCVState *env, target_ulong val,
-                                        target_ulong val)
+                                          uint32_t ctr_idx)
 {
-    int ctr_idx = csrno - CSR_MCYCLE;
     PMUCTRState *counter = &env->pmu_ctrs[ctr_idx];
     uint64_t mhpmctr_val = val;
 
@@ -1252,10 +1266,9 @@ static RISCVException write_mhpmcounter(CPURISCVState *env, int csrno,
     return RISCV_EXCP_NONE;
 }
 
-static RISCVException write_mhpmcounterh(CPURISCVState *env, int csrno,
+static RISCVException riscv_pmu_write_ctrh(CPURISCVState *env, target_ulong val,
-                                         target_ulong val)
+                                          uint32_t ctr_idx)
 {
-    int ctr_idx = csrno - CSR_MCYCLEH;
     PMUCTRState *counter = &env->pmu_ctrs[ctr_idx];
     uint64_t mhpmctr_val = counter->mhpmcounter_val;
     uint64_t mhpmctrh_val = val;
@@ -1277,6 +1290,20 @@ static RISCVException write_mhpmcounterh(CPURISCVState *env, int csrno,
     return RISCV_EXCP_NONE;
 }
 
+static int write_mhpmcounter(CPURISCVState *env, int csrno, target_ulong val)
+{
+    int ctr_idx = csrno - CSR_MCYCLE;
+
+    return riscv_pmu_write_ctr(env, val, ctr_idx);
+}
+
+static int write_mhpmcounterh(CPURISCVState *env, int csrno, target_ulong val)
+{
+    int ctr_idx = csrno - CSR_MCYCLEH;
+
+    return riscv_pmu_write_ctrh(env, val, ctr_idx);
+}
+
 RISCVException riscv_pmu_read_ctr(CPURISCVState *env, target_ulong *val,
                                          bool upper_half, uint32_t ctr_idx)
 {
@@ -1342,6 +1369,167 @@ static RISCVException read_hpmcounterh(CPURISCVState *env, int csrno,
     return riscv_pmu_read_ctr(env, val, true, ctr_index);
 }
 
+static int rmw_cd_mhpmcounter(CPURISCVState *env, int ctr_idx,
+                              target_ulong *val, target_ulong new_val,
+                              target_ulong wr_mask)
+{
+    if (wr_mask != 0 && wr_mask != -1) {
+        return -EINVAL;
+    }
+
+    if (!wr_mask && val) {
+        riscv_pmu_read_ctr(env, val, false, ctr_idx);
+    } else if (wr_mask) {
+        riscv_pmu_write_ctr(env, new_val, ctr_idx);
+    } else {
+        return -EINVAL;
+    }
+
+    return 0;
+}
+
+static int rmw_cd_mhpmcounterh(CPURISCVState *env, int ctr_idx,
+                               target_ulong *val, target_ulong new_val,
+                               target_ulong wr_mask)
+{
+    if (wr_mask != 0 && wr_mask != -1) {
+        return -EINVAL;
+    }
+
+    if (!wr_mask && val) {
+        riscv_pmu_read_ctr(env, val, true, ctr_idx);
+    } else if (wr_mask) {
+        riscv_pmu_write_ctrh(env, new_val, ctr_idx);
+    } else {
+        return -EINVAL;
+    }
+
+    return 0;
+}
+
+static int rmw_cd_mhpmevent(CPURISCVState *env, int evt_index,
+                            target_ulong *val, target_ulong new_val,
+                            target_ulong wr_mask)
+{
+    uint64_t mhpmevt_val = new_val;
+
+    if (wr_mask != 0 && wr_mask != -1) {
+        return -EINVAL;
+    }
+
+    if (!wr_mask && val) {
+        *val = env->mhpmevent_val[evt_index];
+        if (riscv_cpu_cfg(env)->ext_sscofpmf) {
+            *val &= ~MHPMEVENT_BIT_MINH;
+        }
+    } else if (wr_mask) {
+        wr_mask &= ~MHPMEVENT_BIT_MINH;
+        mhpmevt_val = (new_val & wr_mask) |
+                      (env->mhpmevent_val[evt_index] & ~wr_mask);
+        if (riscv_cpu_mxl(env) == MXL_RV32) {
+            mhpmevt_val = mhpmevt_val |
+                          ((uint64_t)env->mhpmeventh_val[evt_index] << 32);
+        }
+        env->mhpmevent_val[evt_index] = mhpmevt_val;
+        riscv_pmu_update_event_map(env, mhpmevt_val, evt_index);
+    } else {
+        return -EINVAL;
+    }
+
+    return 0;
+}
+
+static int rmw_cd_mhpmeventh(CPURISCVState *env, int evt_index,
+                             target_ulong *val, target_ulong new_val,
+                             target_ulong wr_mask)
+{
+    uint64_t mhpmevth_val;
+    uint64_t mhpmevt_val = env->mhpmevent_val[evt_index];
+
+    if (wr_mask != 0 && wr_mask != -1) {
+        return -EINVAL;
+    }
+
+    if (!wr_mask && val) {
+        *val = env->mhpmeventh_val[evt_index];
+        if (riscv_cpu_cfg(env)->ext_sscofpmf) {
+            *val &= ~MHPMEVENTH_BIT_MINH;
+        }
+    } else if (wr_mask) {
+        wr_mask &= ~MHPMEVENTH_BIT_MINH;
+        env->mhpmeventh_val[evt_index] =
+            (new_val & wr_mask) | (env->mhpmeventh_val[evt_index] & ~wr_mask);
+        mhpmevth_val = env->mhpmeventh_val[evt_index];
+        mhpmevt_val = mhpmevt_val | (mhpmevth_val << 32);
+        riscv_pmu_update_event_map(env, mhpmevt_val, evt_index);
+    } else {
+        return -EINVAL;
+    }
+
+    return 0;
+}
+
+static int rmw_cd_ctr_cfg(CPURISCVState *env, int cfg_index, target_ulong *val,
+                            target_ulong new_val, target_ulong wr_mask)
+{
+    switch (cfg_index) {
+    case 0:             /* CYCLECFG */
+        if (wr_mask) {
+            wr_mask &= ~MCYCLECFG_BIT_MINH;
+            env->mcyclecfg = (new_val & wr_mask) | (env->mcyclecfg & ~wr_mask);
+        } else {
+            *val = env->mcyclecfg &= ~MHPMEVENTH_BIT_MINH;
+        }
+        break;
+    case 2:             /* INSTRETCFG */
+        if (wr_mask) {
+            wr_mask &= ~MINSTRETCFG_BIT_MINH;
+            env->minstretcfg = (new_val & wr_mask) |
+                               (env->minstretcfg & ~wr_mask);
+        } else {
+            *val = env->minstretcfg &= ~MHPMEVENTH_BIT_MINH;
+        }
+        break;
+    default:
+        return -EINVAL;
+    }
+    return 0;
+}
+
+static int rmw_cd_ctr_cfgh(CPURISCVState *env, int cfg_index, target_ulong *val,
+                            target_ulong new_val, target_ulong wr_mask)
+{
+
+    if (riscv_cpu_mxl(env) != MXL_RV32) {
+        return RISCV_EXCP_ILLEGAL_INST;
+    }
+
+    switch (cfg_index) {
+    case 0:         /* CYCLECFGH */
+        if (wr_mask) {
+            wr_mask &= ~MCYCLECFGH_BIT_MINH;
+            env->mcyclecfgh = (new_val & wr_mask) |
+                              (env->mcyclecfgh & ~wr_mask);
+        } else {
+            *val = env->mcyclecfgh;
+        }
+        break;
+    case 2:          /* INSTRETCFGH */
+        if (wr_mask) {
+            wr_mask &= ~MINSTRETCFGH_BIT_MINH;
+            env->minstretcfgh = (new_val & wr_mask) |
+                                (env->minstretcfgh & ~wr_mask);
+        } else {
+            *val = env->minstretcfgh;
+        }
+        break;
+    default:
+        return -EINVAL;
+    }
+    return 0;
+}
+
+
 static RISCVException read_scountovf(CPURISCVState *env, int csrno,
                                      target_ulong *val)
 {
@@ -1351,6 +1539,14 @@ static RISCVException read_scountovf(CPURISCVState *env, int csrno,
     target_ulong *mhpm_evt_val;
     uint64_t of_bit_mask;
 
+    /* Virtualize scountovf for counter delegation */
+    if (riscv_cpu_cfg(env)->ext_sscofpmf &&
+        riscv_cpu_cfg(env)->ext_ssccfg &&
+        get_field(env->menvcfg, MENVCFG_CDE) &&
+        env->virt_enabled) {
+        return RISCV_EXCP_VIRT_INSTRUCTION_FAULT;
+    }
+
     if (riscv_cpu_mxl(env) == MXL_RV32) {
         mhpm_evt_val = env->mhpmeventh_val;
         of_bit_mask = MHPMEVENTH_BIT_OF;
@@ -2293,11 +2489,72 @@ static int rmw_xireg_cd(CPURISCVState *env, int csrno,
                         target_ulong isel, target_ulong *val,
                         target_ulong new_val, target_ulong wr_mask)
 {
-    if (!riscv_cpu_cfg(env)->ext_smcdeleg) {
+    int ret = -EINVAL;
-        return RISCV_EXCP_ILLEGAL_INST;
+    int ctr_index = isel - ISELECT_CD_FIRST;
+    int isel_hpm_start = ISELECT_CD_FIRST + 3;
+
+    if (!riscv_cpu_cfg(env)->ext_smcdeleg || !riscv_cpu_cfg(env)->ext_ssccfg) {
+        ret = RISCV_EXCP_ILLEGAL_INST;
+        goto done;
     }
-    /* TODO: Implement the functionality later */
+
-    return RISCV_EXCP_NONE;
+    /* Invalid siselect value for reserved */
+    if (ctr_index == 1) {
+        goto done;
+    }
+
+    /* sireg4 and sireg5 provides access RV32 only CSRs */
+    if (((csrno == CSR_SIREG5) || (csrno == CSR_SIREG4)) &&
+        (riscv_cpu_mxl(env) != MXL_RV32)) {
+        ret = RISCV_EXCP_ILLEGAL_INST;
+        goto done;
+    }
+
+    /* Check Sscofpmf dependancy */
+    if (!riscv_cpu_cfg(env)->ext_sscofpmf && csrno == CSR_SIREG5 &&
+        (isel_hpm_start <= isel && isel <= ISELECT_CD_LAST)) {
+        goto done;
+    }
+
+    /* Check smcntrpmf dependancy */
+    if (!riscv_cpu_cfg(env)->ext_smcntrpmf &&
+        (csrno == CSR_SIREG2 || csrno == CSR_SIREG5) &&
+        (ISELECT_CD_FIRST <= isel && isel < isel_hpm_start)) {
+        goto done;
+    }
+
+    if (!get_field(env->mcounteren, BIT(ctr_index)) ||
+        !get_field(env->menvcfg, MENVCFG_CDE)) {
+        goto done;
+    }
+
+    switch (csrno) {
+    case CSR_SIREG:
+        ret = rmw_cd_mhpmcounter(env, ctr_index, val, new_val, wr_mask);
+        break;
+    case CSR_SIREG4:
+        ret = rmw_cd_mhpmcounterh(env, ctr_index, val, new_val, wr_mask);
+        break;
+    case CSR_SIREG2:
+        if (ctr_index <= 2) {
+            ret = rmw_cd_ctr_cfg(env, ctr_index, val, new_val, wr_mask);
+        } else {
+            ret = rmw_cd_mhpmevent(env, ctr_index, val, new_val, wr_mask);
+        }
+        break;
+    case CSR_SIREG5:
+        if (ctr_index <= 2) {
+            ret = rmw_cd_ctr_cfgh(env, ctr_index, val, new_val, wr_mask);
+        } else {
+            ret = rmw_cd_mhpmeventh(env, ctr_index, val, new_val, wr_mask);
+        }
+        break;
+    default:
+        goto done;
+    }
+
+done:
+    return ret;
 }
 
 /*
@@ -2576,6 +2833,21 @@ static RISCVException write_mcountinhibit(CPURISCVState *env, int csrno,
     return RISCV_EXCP_NONE;
 }
 
+static RISCVException read_scountinhibit(CPURISCVState *env, int csrno,
+                                         target_ulong *val)
+{
+    /* S-mode can only access the bits delegated by M-mode */
+    *val = env->mcountinhibit & env->mcounteren;
+    return RISCV_EXCP_NONE;
+}
+
+static RISCVException write_scountinhibit(CPURISCVState *env, int csrno,
+                                          target_ulong val)
+{
+    write_mcountinhibit(env, csrno, val & env->mcounteren);
+    return RISCV_EXCP_NONE;
+}
+
 static RISCVException read_mcounteren(CPURISCVState *env, int csrno,
                                       target_ulong *val)
 {
@@ -2678,11 +2950,13 @@ static RISCVException write_menvcfg(CPURISCVState *env, int csrno,
                                     target_ulong val)
 {
     const RISCVCPUConfig *cfg = riscv_cpu_cfg(env);
-    uint64_t mask = MENVCFG_FIOM | MENVCFG_CBIE | MENVCFG_CBCFE | MENVCFG_CBZE;
+    uint64_t mask = MENVCFG_FIOM | MENVCFG_CBIE | MENVCFG_CBCFE |
+                    MENVCFG_CBZE | MENVCFG_CDE;
 
     if (riscv_cpu_mxl(env) == MXL_RV64) {
         mask |= (cfg->ext_svpbmt ? MENVCFG_PBMTE : 0) |
                 (cfg->ext_sstc ? MENVCFG_STCE : 0) |
+                (cfg->ext_smcdeleg ? MENVCFG_CDE : 0) |
                 (cfg->ext_svadu ? MENVCFG_ADUE : 0);
 
         if (env_archcpu(env)->cfg.ext_zicfilp) {
@@ -2717,7 +2991,8 @@ static RISCVException write_menvcfgh(CPURISCVState *env, int csrno,
     const RISCVCPUConfig *cfg = riscv_cpu_cfg(env);
     uint64_t mask = (cfg->ext_svpbmt ? MENVCFG_PBMTE : 0) |
                     (cfg->ext_sstc ? MENVCFG_STCE : 0) |
-                    (cfg->ext_svadu ? MENVCFG_ADUE : 0);
+                    (cfg->ext_svadu ? MENVCFG_ADUE : 0) |
+                    (cfg->ext_smcdeleg ? MENVCFG_CDE : 0);
     uint64_t valh = (uint64_t)val << 32;
 
     env->menvcfg = (env->menvcfg & ~mask) | (valh & mask);
@@ -5304,6 +5579,11 @@ riscv_csr_operations csr_ops[CSR_TABLE_SIZE] = {
     [CSR_MNSTATUS]  = { "mnstatus",  rnmi, read_mnstatus,  write_mnstatus,
                         .min_priv_ver = PRIV_VERSION_1_12_0               },
 
+    /* Supervisor Counter Delegation */
+    [CSR_SCOUNTINHIBIT] = {"scountinhibit", scountinhibit_pred,
+                            read_scountinhibit, write_scountinhibit,
+                           .min_priv_ver = PRIV_VERSION_1_12_0 },
+
     /* Supervisor Trap Setup */
     [CSR_SSTATUS]    = { "sstatus",    smode, read_sstatus,    write_sstatus,
                          NULL,                read_sstatus_i128              },