Re: [PATCH] target/riscv/csr.c: fix H extension TVM trap

[LIU Zhiwei]

On 2023/3/8 20:34, chenyi2...@zju.edu.cn wrote:
From: Yi Chen<chenyi2...@zju.edu.cn>
Trap accesses to hgatp if MSTATUS_TVM is enabled.
Don't trap accesses to vsatp even if MSTATUS_TVM is enabled.

By the way, do you know why mstatus_tvm and hstatus_tvm are needed?

The specification said,

The TVM mechanism improves virtualization efficiency by permitting guest 
operating systems to
execute in S-mode, rather than classically virtualizing them in U-mode. This 
approach obviates
the need to trap accesses to most S-mode CSRs.

I don't know how the tvm field obviates the need to trap accesses to 
most S-mode CSRs.

Thanks,
Zhiwei


Signed-off-by: Yi Chen<chenyi2...@zju.edu.cn>
---
  target/riscv/csr.c | 18 ++++++++++++++----
  1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/target/riscv/csr.c b/target/riscv/csr.c
index ab56663..09bc780 100644
--- a/target/riscv/csr.c
+++ b/target/riscv/csr.c
@@ -2655,7 +2655,7 @@ static RISCVException read_satp(CPURISCVState *env, int 
csrno,
          return RISCV_EXCP_NONE;
      }
  
-    if (env->priv == PRV_S && get_field(env->mstatus, MSTATUS_TVM)) {
+    if (env->priv == PRV_S && !riscv_cpu_virt_enabled(env) && 
get_field(env->mstatus, MSTATUS_TVM)) {
          return RISCV_EXCP_ILLEGAL_INST;
      } else {
          *val = env->satp;
@@ -2683,7 +2683,7 @@ static RISCVException write_satp(CPURISCVState *env, int 
csrno,
      }
  
      if (vm && mask) {
-        if (env->priv == PRV_S && get_field(env->mstatus, MSTATUS_TVM)) {
+        if (env->priv == PRV_S && !riscv_cpu_virt_enabled(env) && 
get_field(env->mstatus, MSTATUS_TVM)) {
              return RISCV_EXCP_ILLEGAL_INST;
          } else {
              /*
@@ -3047,14 +3047,24 @@ static RISCVException read_hgeip(CPURISCVState *env, 
int csrno,
  static RISCVException read_hgatp(CPURISCVState *env, int csrno,
                                   target_ulong *val)
  {
-    *val = env->hgatp;
+    if (env->priv == PRV_S && get_field(env->mstatus, MSTATUS_TVM)) {
+        return RISCV_EXCP_ILLEGAL_INST;
+    } else {
+        *val = env->hgatp;
+    }
+
      return RISCV_EXCP_NONE;
  }
  
  static RISCVException write_hgatp(CPURISCVState *env, int csrno,
                                    target_ulong val)
  {
-    env->hgatp = val;
+    if (env->priv == PRV_S && get_field(env->mstatus, MSTATUS_TVM)) {
+        return RISCV_EXCP_ILLEGAL_INST;
+    } else {
+        env->hgatp = val;
+    }
+
      return RISCV_EXCP_NONE;
  }