Re: [PATCH v2] target/riscv/pmp: Raise exception if no PMP entry is configured

[Alistair Francis <alistair23@gmail.com>]

On Wed, Dec 23, 2020 at 11:26 AM Atish Patra <atish.patra@wdc.com> wrote:
>
> As per the privilege specification, any access from S/U mode should fail
> if no pmp region is configured.

This doesn't sound right, the spec says:

"If no PMP entry matches an S-mode or U-mode access, but at least one
PMP entry is implemented, the access fails."

I don't see anything saying that an access will fail if there are no
PMP regions configred.

Alistair

>
> Signed-off-by: Atish Patra <atish.patra@wdc.com>
> ---
> Changes from v2->v1
> 1. Removed the static from the function definition
> ---
>  target/riscv/op_helper.c | 5 +++++
>  target/riscv/pmp.c       | 4 ++--
>  target/riscv/pmp.h       | 1 +
>  3 files changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/target/riscv/op_helper.c b/target/riscv/op_helper.c
> index d55def76cffd..1eddcb94de7e 100644
> --- a/target/riscv/op_helper.c
> +++ b/target/riscv/op_helper.c
> @@ -150,6 +150,11 @@ target_ulong helper_mret(CPURISCVState *env, target_ulong cpu_pc_deb)
>
>      uint64_t mstatus = env->mstatus;
>      target_ulong prev_priv = get_field(mstatus, MSTATUS_MPP);
> +
> +    if (!pmp_get_num_rules(env) && (prev_priv != PRV_M)) {
> +        riscv_raise_exception(env, RISCV_EXCP_ILLEGAL_INST, GETPC());
> +    }
> +
>      target_ulong prev_virt = get_field(env->mstatus, MSTATUS_MPV);
>      mstatus = set_field(mstatus, MSTATUS_MIE,
>                          get_field(mstatus, MSTATUS_MPIE));
> diff --git a/target/riscv/pmp.c b/target/riscv/pmp.c
> index 2eda8e1e2f07..80d0334e1bfc 100644
> --- a/target/riscv/pmp.c
> +++ b/target/riscv/pmp.c
> @@ -74,7 +74,7 @@ static inline int pmp_is_locked(CPURISCVState *env, uint32_t pmp_index)
>  /*
>   * Count the number of active rules.
>   */
> -static inline uint32_t pmp_get_num_rules(CPURISCVState *env)
> +uint32_t pmp_get_num_rules(CPURISCVState *env)
>  {
>       return env->pmp_state.num_rules;
>  }
> @@ -237,7 +237,7 @@ bool pmp_hart_has_privs(CPURISCVState *env, target_ulong addr,
>
>      /* Short cut if no rules */
>      if (0 == pmp_get_num_rules(env)) {
> -        return true;
> +        return (env->priv == PRV_M) ? true : false;
>      }
>
>      if (size == 0) {
> diff --git a/target/riscv/pmp.h b/target/riscv/pmp.h
> index 6c6b4c9befe8..c8d5ef4a694e 100644
> --- a/target/riscv/pmp.h
> +++ b/target/riscv/pmp.h
> @@ -64,5 +64,6 @@ bool pmp_is_range_in_tlb(CPURISCVState *env, hwaddr tlb_sa,
>                           target_ulong *tlb_size);
>  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);
>
>  #endif
> --
> 2.25.1
>
>