Re: [PATCH] target/riscv: pmp: Clear pmp/smepmp bits on reset

[Vladimir Isaev]

Hi Mayuresh,

25.09.2023 14:09, Mayuresh Chitale wrote:
> As per the Priv and Smepmp specifications, certain bits such as the 'L'
> bit of pmp entries and mseccfg.MML can only be cleared upon reset and it
> is necessary to do so to allow 'M' mode firmware to correctly reinitialize
> the pmp/smpemp state across reboots.
> 
> Signed-off-by: Mayuresh Chitale <mchitale@ventanamicro.com>
> ---
>  target/riscv/cpu.c | 11 +++++++++++
>  target/riscv/pmp.c | 10 ++++++++++
>  target/riscv/pmp.h |  1 +
>  3 files changed, 22 insertions(+)
> 
> diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
> index 0fb01788e7..561567651e 100644
> --- a/target/riscv/cpu.c
> +++ b/target/riscv/cpu.c
> @@ -761,6 +761,17 @@ static void riscv_cpu_reset_hold(Object *obj)
>      }
>      /* mmte is supposed to have pm.current hardwired to 1 */
>      env->mmte |= (EXT_STATUS_INITIAL | MMTE_M_PM_CURRENT);
> +
> +    /*
> +     * Clear mseccfg and unlock all the PMP entries upon reset.
> +     * This is allowed as per the priv and smepmp specifications
> +     * and is needed to clear stale entries across reboots.
> +     */
> +    if (riscv_cpu_cfg(env)->ext_smepmp) {
> +        env->mseccfg = 0;
> +    }
> +
> +    pmp_unlock_entries(env);
>  #endif
>      env->xl = riscv_cpu_mxl(env);
>      riscv_cpu_update_mask(env);
> diff --git a/target/riscv/pmp.c b/target/riscv/pmp.c
> index f498e414f0..5b14eb511a 100644
> --- a/target/riscv/pmp.c
> +++ b/target/riscv/pmp.c
> @@ -129,6 +129,16 @@ static void pmp_write_cfg(CPURISCVState *env, uint32_t 
> pmp_index, uint8_t val)
>      }
>  }
> 
> +void pmp_unlock_entries(CPURISCVState *env)
> +{
> +    uint32_t pmp_num = pmp_get_num_rules(env);
> +    int i;
> +
> +    for (i = 0; i < pmp_num; i++) {
> +        env->pmp_state.pmp[i].cfg_reg &= ~PMP_LOCK;

According to spec:

Writable PMP registers’ A and L fields are set to 0, unless the
platform mandates a different reset value for some PMP registers’ A and L 
fields.

So should we also set PMP_AMATCH_OFF in cfg?

Thank you,
Vladimir Isaev

> +    }
> +}
> +
>  static void pmp_decode_napot(target_ulong a, target_ulong *sa,
>                               target_ulong *ea)
>  {
> diff --git a/target/riscv/pmp.h b/target/riscv/pmp.h
> index b296ea1fc6..0ab60fe15f 100644
> --- a/target/riscv/pmp.h
> +++ b/target/riscv/pmp.h
> @@ -82,6 +82,7 @@ void pmp_update_rule_addr(CPURISCVState *env, uint32_t 
> pmp_index);
>  void pmp_update_rule_nums(CPURISCVState *env);
>  uint32_t pmp_get_num_rules(CPURISCVState *env);
>  int pmp_priv_to_page_prot(pmp_priv_t pmp_priv);
> +void pmp_unlock_entries(CPURISCVState *env);
> 
>  #define MSECCFG_MML_ISSET(env) get_field(env->mseccfg, MSECCFG_MML)
>  #define MSECCFG_MMWP_ISSET(env) get_field(env->mseccfg, MSECCFG_MMWP)
> --
> 2.34.1
> 
>