Re: [PATCH 1/2] target/riscv: Fix the mstatus.MPP value after executing MRET

[Alistair Francis <alistair23@gmail.com>]

On Thu, Mar 30, 2023 at 11:59 PM Weiwei Li <liweiwei@iscas.ac.cn> wrote:
>
> The MPP will be set to the least-privileged supported mode (U if
> U-mode is implemented, else M).

I don't think this is right, the spec in section 8.6.4 says this:

"MRET then in mstatus/mstatush sets MPV=0, MPP=0,
MIE=MPIE, and MPIE=1"

So it should just always be 0 (PRV_U is 0)

Alistair

>
> Signed-off-by: Weiwei Li <liweiwei@iscas.ac.cn>
> Signed-off-by: Junqiang Wang <wangjunqiang@iscas.ac.cn>
> ---
>  target/riscv/op_helper.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/target/riscv/op_helper.c b/target/riscv/op_helper.c
> index 84ee018f7d..991f06d98d 100644
> --- a/target/riscv/op_helper.c
> +++ b/target/riscv/op_helper.c
> @@ -339,7 +339,8 @@ target_ulong helper_mret(CPURISCVState *env)
>      mstatus = set_field(mstatus, MSTATUS_MIE,
>                          get_field(mstatus, MSTATUS_MPIE));
>      mstatus = set_field(mstatus, MSTATUS_MPIE, 1);
> -    mstatus = set_field(mstatus, MSTATUS_MPP, PRV_U);
> +    mstatus = set_field(mstatus, MSTATUS_MPP,
> +                        riscv_has_ext(env, RVU) ? PRV_U : PRV_M);
>      mstatus = set_field(mstatus, MSTATUS_MPV, 0);
>      if ((env->priv_ver >= PRIV_VERSION_1_12_0) && (prev_priv != PRV_M)) {
>          mstatus = set_field(mstatus, MSTATUS_MPRV, 0);
> --
> 2.25.1
>
>