target/riscv: Add select value range check for counter delegation

This adds checks in ops performed on xireg and xireg2-xireg6 so that the
counter delegation function will receive a valid xiselect value with the
proper extensions enabled.

Co-developed-by: Atish Patra <atishp@rivosinc.com>
Signed-off-by: Kaiwen Xue <kaiwenx@rivosinc.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Atish Patra <atishp@rivosinc.com>
Message-ID: <20250110-counter_delegation-v5-7-e83d797ae294@rivosinc.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

1 files changed, 35 insertions, 1 deletions

diff --git a/target/riscv/csr.c b/target/riscv/csr.c
index 49648dd..df748df 100644
--- a/target/riscv/csr.c
+++ b/target/riscv/csr.c
@@ -2159,6 +2159,11 @@ static bool xiselect_aia_range(target_ulong isel)
            (ISELECT_IMSIC_FIRST <= isel && isel <= ISELECT_IMSIC_LAST);
 }
 
+static bool xiselect_cd_range(target_ulong isel)
+{
+    return (ISELECT_CD_FIRST <= isel && isel <= ISELECT_CD_LAST);
+}
+
 static int rmw_iprio(target_ulong xlen,
                      target_ulong iselect, uint8_t *iprio,
                      target_ulong *val, target_ulong new_val,
@@ -2284,6 +2289,17 @@ done:
     return RISCV_EXCP_NONE;
 }
 
+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) {
+        return RISCV_EXCP_ILLEGAL_INST;
+    }
+    /* TODO: Implement the functionality later */
+    return RISCV_EXCP_NONE;
+}
+
 /*
  * rmw_xireg_csrind: Perform indirect access to xireg and xireg2-xireg6
  *
@@ -2295,7 +2311,25 @@ static int rmw_xireg_csrind(CPURISCVState *env, int csrno,
                               target_ulong isel, target_ulong *val,
                               target_ulong new_val, target_ulong wr_mask)
 {
-    return -EINVAL;
+    int ret = -EINVAL;
+    bool virt = csrno == CSR_VSIREG ? true : false;
+
+    if (xiselect_cd_range(isel)) {
+        ret = rmw_xireg_cd(env, csrno, isel, val, new_val, wr_mask);
+    } else {
+        /*
+         * As per the specification, access to unimplented region is undefined
+         * but recommendation is to raise illegal instruction exception.
+         */
+        return RISCV_EXCP_ILLEGAL_INST;
+    }
+
+    if (ret) {
+        return (env->virt_enabled && virt) ?
+               RISCV_EXCP_VIRT_INSTRUCTION_FAULT : RISCV_EXCP_ILLEGAL_INST;
+    }
+
+    return RISCV_EXCP_NONE;
 }
 
 static int rmw_xiregi(CPURISCVState *env, int csrno, target_ulong *val,