target/riscv: pmp: Ignore writes when RW=01

As per the Priv spec: "The R, W, and X fields form a collective WARL
field for which the combinations with R=0 and W=1 are reserved."
However currently such writes are not ignored as ought to be. The
combinations with RW=01 are allowed only when the Smepmp extension
is enabled and mseccfg.MML is set.

Signed-off-by: Mayuresh Chitale <mchitale@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20231019065705.1431868-1-mchitale@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

target/riscv/pmp.c

@@ -123,6 +123,11 @@ static bool pmp_write_cfg(CPURISCVState *env, uint32_t pmp_index, uint8_t val)
         if (locked) {
             qemu_log_mask(LOG_GUEST_ERROR, "ignoring pmpcfg write - locked\n");
         } else if (env->pmp_state.pmp[pmp_index].cfg_reg != val) {
+            /* If !mseccfg.MML then ignore writes with encoding RW=01 */
+            if ((val & PMP_WRITE) && !(val & PMP_READ) &&
+                !MSECCFG_MML_ISSET(env)) {
+                val &= ~(PMP_WRITE | PMP_READ);
+            }
             env->pmp_state.pmp[pmp_index].cfg_reg = val;
             pmp_update_rule_addr(env, pmp_index);
             return true;