[PATCH 6/6] target/riscv: simplify the check in hmode to resue the check in riscv_csrrw_check

[Weiwei Li <liweiwei@iscas.ac.cn>]

Just add 1 to the effective privledge level when in HS mode, then reuse the check
'effective_priv < csr_priv' in riscv_csrrw_check to replace the privilege level
related check in hmode. Then, hmode will only check whether H extension is supported.

when accessing Hypervior CSRs:
   1) if access from M privilege level, the check of 'effective_priv < csr_priv'
passes, returns hmode(...) which will return RISCV_EXCP_ILLEGAL_INST when H
extension is not supported and return RISCV_EXCP_NONE otherwise.
   2) if access from HS privilege level, effective_priv will add 1, the check
passes too, also returns hmode(...) too.
   3) if access from VS/VU privilege level, the check fails, and returns
RISCV_EXCP_VIRT_INSTRUCTION_FAULT
   4) if access from U privilege level, the check fails, and returns
RISCV_EXCP_ILLEGAL_INST

Signed-off-by: Weiwei Li <liweiwei@iscas.ac.cn>
Signed-off-by: Junqiang Wang <wangjunqiang@iscas.ac.cn>
---
 target/riscv/csr.c | 18 +++++-------------
 1 file changed, 5 insertions(+), 13 deletions(-)

diff --git a/target/riscv/csr.c b/target/riscv/csr.c
index 975007f1ac..2b3ed94366 100644
--- a/target/riscv/csr.c
+++ b/target/riscv/csr.c
@@ -312,13 +312,7 @@ static int aia_smode32(CPURISCVState *env, int csrno)
 static RISCVException hmode(CPURISCVState *env, int csrno)
 {
     if (riscv_has_ext(env, RVH)) {
-        /* Hypervisor extension is supported */
-        if ((env->priv == PRV_S && !riscv_cpu_virt_enabled(env)) ||
-            env->priv == PRV_M) {
-            return RISCV_EXCP_NONE;
-        } else {
-            return RISCV_EXCP_VIRT_INSTRUCTION_FAULT;
-        }
+        return RISCV_EXCP_NONE;
     }
 
     return RISCV_EXCP_ILLEGAL_INST;
@@ -3280,13 +3274,11 @@ static inline RISCVException riscv_csrrw_check(CPURISCVState *env,
 #if !defined(CONFIG_USER_ONLY)
     int csr_priv, effective_priv = env->priv;
 
-    if (riscv_has_ext(env, RVH) && env->priv == PRV_S) {
+    if (riscv_has_ext(env, RVH) && env->priv == PRV_S &&
+        !riscv_cpu_virt_enabled(env)) {
         /*
-         * We are in either HS or VS mode.
-         * Add 1 to the effective privledge level to allow us to access the
-         * Hypervisor CSRs. The `hmode` predicate will determine if access
-         * should be allowed(HS) or if a virtual instruction exception should be
-         * raised(VS).
+         * We are in HS mode. Add 1 to the effective privledge level to
+         * allow us to access the Hypervisor CSRs.
          */
         effective_priv++;
     }
-- 
2.17.1