[PATCH] target/riscv: Fix priority of csr related check in riscv_csrrw_check

[Weiwei Li]

Normally, riscv_csrrw_check is called when executing Zicsr instructions.
And we can only do access control for existed CSRs. So the priority of
CSR related check, from highest to lowest, should be as follows:
1) check whether Zicsr is supported: raise RISCV_EXCP_ILLEGAL_INST if not
2) check whether csr is existed: raise RISCV_EXCP_ILLEGAL_INST if not
3) do access control: raise RISCV_EXCP_ILLEGAL_INST or RISCV_EXCP_VIRT_
INSTRUCTION_FAULT if not allowed

The predicates contain parts of function of both 2) and 3), So they need
to be placed in the middle of riscv_csrrw_check

Signed-off-by: Weiwei Li <liweiwei@iscas.ac.cn>
Signed-off-by: Junqiang Wang <wangjunqiang@iscas.ac.cn>
---
 target/riscv/csr.c | 44 +++++++++++++++++++++++++-------------------
 1 file changed, 25 insertions(+), 19 deletions(-)

diff --git a/target/riscv/csr.c b/target/riscv/csr.c
index 0fb042b2fd..d81f466c80 100644
--- a/target/riscv/csr.c
+++ b/target/riscv/csr.c
@@ -3270,6 +3270,30 @@ static inline RISCVException 
riscv_csrrw_check(CPURISCVState *env,
     /* check privileges and return RISCV_EXCP_ILLEGAL_INST if check fails */
     int read_only = get_field(csrno, 0xC00) == 3;
     int csr_min_priv = csr_ops[csrno].min_priv_ver;
+
+    /* ensure the CSR extension is enabled. */
+    if (!cpu->cfg.ext_icsr) {
+        return RISCV_EXCP_ILLEGAL_INST;
+    }
+
+    if (env->priv_ver < csr_min_priv) {
+        return RISCV_EXCP_ILLEGAL_INST;
+    }
+
+    /* check predicate */
+    if (!csr_ops[csrno].predicate) {
+        return RISCV_EXCP_ILLEGAL_INST;
+    }
+
+    if (write_mask && read_only) {
+        return RISCV_EXCP_ILLEGAL_INST;
+    }
+
+    RISCVException ret = csr_ops[csrno].predicate(env, csrno);
+    if (ret != RISCV_EXCP_NONE) {
+        return ret;
+    }
+
 #if !defined(CONFIG_USER_ONLY)
     int csr_priv, effective_priv = env->priv;
 
@@ -3290,25 +3314,7 @@ static inline RISCVException 
riscv_csrrw_check(CPURISCVState *env,
         return RISCV_EXCP_ILLEGAL_INST;
     }
 #endif
-    if (write_mask && read_only) {
-        return RISCV_EXCP_ILLEGAL_INST;
-    }
-
-    /* ensure the CSR extension is enabled. */
-    if (!cpu->cfg.ext_icsr) {
-        return RISCV_EXCP_ILLEGAL_INST;
-    }
-
-    /* check predicate */
-    if (!csr_ops[csrno].predicate) {
-        return RISCV_EXCP_ILLEGAL_INST;
-    }
-
-    if (env->priv_ver < csr_min_priv) {
-        return RISCV_EXCP_ILLEGAL_INST;
-    }
-
-    return csr_ops[csrno].predicate(env, csrno);
+    return RISCV_EXCP_NONE;
 }
 
 static RISCVException riscv_csrrw_do64(CPURISCVState *env, int csrno,
-- 
2.17.1