Re: [PATCH] target/riscv: Fix mcycle/minstret increment behavior

[Alistair Francis]

On Tue, Dec 26, 2023 at 3:29 PM Xu Lu <luxu.kernel@bytedance.com> wrote:
>
> The mcycle/minstret counter's stop flag is mistakenly updated on a copy
> on stack. Thus the counter increments even when the CY/IR bit in the
> mcountinhibit register is set. This commit corrects its behavior.
>
> Fixes: 3780e33732f88 (target/riscv: Support mcycle/minstret write operation)
> Signed-off-by: Xu Lu <luxu.kernel@bytedance.com>

Reviewed-by: Alistair Francis <alistair.francis@wdc.com>

Alistair

> ---
>  target/riscv/csr.c | 14 +++++++-------
>  1 file changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/target/riscv/csr.c b/target/riscv/csr.c
> index fde7ce1a5336..c50a33397c51 100644
> --- a/target/riscv/csr.c
> +++ b/target/riscv/csr.c
> @@ -907,11 +907,11 @@ static int write_mhpmcounterh(CPURISCVState *env, int 
> csrno, target_ulong val)
>  static RISCVException riscv_pmu_read_ctr(CPURISCVState *env, target_ulong 
> *val,
>                                           bool upper_half, uint32_t ctr_idx)
>  {
> -    PMUCTRState counter = env->pmu_ctrs[ctr_idx];
> -    target_ulong ctr_prev = upper_half ? counter.mhpmcounterh_prev :
> -                                         counter.mhpmcounter_prev;
> -    target_ulong ctr_val = upper_half ? counter.mhpmcounterh_val :
> -                                        counter.mhpmcounter_val;
> +    PMUCTRState *counter = &env->pmu_ctrs[ctr_idx];
> +    target_ulong ctr_prev = upper_half ? counter->mhpmcounterh_prev :
> +                                         counter->mhpmcounter_prev;
> +    target_ulong ctr_val = upper_half ? counter->mhpmcounterh_val :
> +                                        counter->mhpmcounter_val;
>
>      if (get_field(env->mcountinhibit, BIT(ctr_idx))) {
>          /*
> @@ -919,12 +919,12 @@ static RISCVException riscv_pmu_read_ctr(CPURISCVState 
> *env, target_ulong *val,
>           * stop the icount counting. Just return the counter value written by
>           * the supervisor to indicate that counter was not incremented.
>           */
> -        if (!counter.started) {
> +        if (!counter->started) {
>              *val = ctr_val;
>              return RISCV_EXCP_NONE;
>          } else {
>              /* Mark that the counter has been stopped */
> -            counter.started = false;
> +            counter->started = false;
>          }
>      }
>
> --
> 2.20.1
>
>