[dv] tb_cs_registers golden-model error in ePMP extension

[ZhongYic00]

Observed Behavior

DV test lowrisc:ibex:tb_cs_registers fails given +ntb_random_seed=111

Error, transaction:
Register transaction:
Operation:  CSR Read
Address:    PMPCfg0
Read data:  6981400
Expected rdata: 6981484
- ../src/lowrisc_ibex_tb_cs_registers_0/tb/tb_cs_registers.sv:111: Verilog $finish
Received $finish() from Verilog, shutting down simulation.
[Reg driver] drove: 4970 register transactions

//-------------//
// TEST FAILED //
//-------------//

Expected Behavior

CS_Registers test should pass, RTL's dealing with mseccfg and pmpcfg is right.
At that point, mseccfg.MML is set, write a new entry with exec privilege to pmpcfg results in no change.

The provided golden-model in base_register.cc is wrong when handling CSRWrite to pmpcfg.
It should first check mseccfg.MML then write, rather than dealing with // No reserved L/R/W/X values when MML Set.

It should check whether the new entry is a "new rule with executable privilege".
This may be due to SMEPMP extension's evolving.

uint32_t PmpCfgRegister::RegisterWrite(uint32_t newval) {
  uint32_t lock_mask = GetLockMask();
  uint32_t read_value = register_value_;

  register_value_ &= lock_mask;
  register_value_ |= (newval & ~lock_mask);
  register_value_ = HandleReservedVals(register_value_);

  return read_value;
}

Steps to reproduce the issue

fusesoc --cores-root=. run --target=sim --tool=verilator lowrisc:ibex:tb_cs_registers --run_options='+
ibex_tracer_enable=1 +ntb_random_seed=0'

My Environment

EDA tool and version:

Verilator 4.210 2021-07-07 rev v4.210

Operating system:

Ubuntu Linux 22.04

Version of the Ibex source code:

8f4c75c