Re: [PATCH v2 4/5] target/riscv: pmp: exit csr writes early if value was not changed

[LIU Zhiwei]

On 2025/3/14 03:30, Loïc Lefort wrote:

Signed-off-by: Loïc Lefort <l...@rivosinc.com>
Reviewed-by: Daniel Henrique Barboza <dbarb...@ventanamicro.com>
---
  target/riscv/pmp.c | 22 +++++++++++++++-------
  1 file changed, 15 insertions(+), 7 deletions(-)

diff --git a/target/riscv/pmp.c b/target/riscv/pmp.c
index c5f6cdaccb..845915e0c8 100644
--- a/target/riscv/pmp.c
+++ b/target/riscv/pmp.c
@@ -141,6 +141,11 @@ static inline uint8_t pmp_read_cfg(CPURISCVState *env, 
uint32_t pmp_index)
  static bool pmp_write_cfg(CPURISCVState *env, uint32_t pmp_index, uint8_t val)
  {
      if (pmp_index < MAX_RISCV_PMPS) {
+        if (env->pmp_state.pmp[pmp_index].cfg_reg == val) {
+            /* no change */
+            return false;
+        }
+
          if (pmp_is_readonly(env, pmp_index)) {
              qemu_log_mask(LOG_GUEST_ERROR,
                            "ignoring pmpcfg write - read only\n");
@@ -528,6 +533,11 @@ void pmpaddr_csr_write(CPURISCVState *env, uint32_t 
addr_index,
      bool is_next_cfg_tor = false;

if (addr_index < MAX_RISCV_PMPS) {

+        if (env->pmp_state.pmp[addr_index].addr_reg == val) {
+            /* no change */
+            return;
+        }
+
          /*
           * In TOR mode, need to check the lock bit of the next pmp
           * (if there is a next).
@@ -544,14 +554,12 @@ void pmpaddr_csr_write(CPURISCVState *env, uint32_t 
addr_index,
          }

if (!pmp_is_readonly(env, addr_index)) {

-            if (env->pmp_state.pmp[addr_index].addr_reg != val) {

Is there some benefit removing this if sentence?

Zhiwei

-                env->pmp_state.pmp[addr_index].addr_reg = val;
-                pmp_update_rule_addr(env, addr_index);
-                if (is_next_cfg_tor) {
-                    pmp_update_rule_addr(env, addr_index + 1);
-                }
-                tlb_flush(env_cpu(env));
+            env->pmp_state.pmp[addr_index].addr_reg = val;
+            pmp_update_rule_addr(env, addr_index);
+            if (is_next_cfg_tor) {
+                pmp_update_rule_addr(env, addr_index + 1);
              }
+            tlb_flush(env_cpu(env));
          } else {
              qemu_log_mask(LOG_GUEST_ERROR,
                            "ignoring pmpaddr write - read only\n");