Re: [PATCH v9 15/20] target/riscv/cpu.c: introduce cpu_cfg_ext_auto_update()

[Alistair Francis <alistair23@gmail.com>]

On Sat, Sep 2, 2023 at 5:49 AM Daniel Henrique Barboza
<dbarboza@ventanamicro.com> wrote:
>
> During realize() time we're activating a lot of extensions based on some
> criteria, e.g.:
>
>     if (cpu->cfg.ext_zk) {
>         cpu->cfg.ext_zkn = true;
>         cpu->cfg.ext_zkr = true;
>         cpu->cfg.ext_zkt = true;
>     }
>
> This practice resulted in at least one case where we ended up enabling
> something we shouldn't: RVC enabling zca/zcd/zcf when using a CPU that
> has priv_spec older than 1.12.0.
>
> We're also not considering user choice. There's no way of doing it now
> but this is about to change in the next few patches.
>
> cpu_cfg_ext_auto_update() will check for priv version mismatches before
> enabling extensions. If we have a mismatch between the current priv
> version and the extension we want to enable, do not enable it. In the
> near future, this same function will also consider user choice when
> deciding if we're going to enable/disable an extension or not.
>
> For now let's use it to handle zca/zcd/zcf enablement if RVC is enabled.
>
> Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>

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

Alistair

> ---
>  target/riscv/cpu.c | 43 ++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 40 insertions(+), 3 deletions(-)
>
> diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
> index 43c68e1792..a4876df5f4 100644
> --- a/target/riscv/cpu.c
> +++ b/target/riscv/cpu.c
> @@ -177,6 +177,43 @@ static void isa_ext_update_enabled(RISCVCPU *cpu, uint32_t ext_offset,
>      *ext_enabled = en;
>  }
>
> +static int cpu_cfg_ext_get_min_version(uint32_t ext_offset)
> +{
> +    int i;
> +
> +    for (i = 0; i < ARRAY_SIZE(isa_edata_arr); i++) {
> +        if (isa_edata_arr[i].ext_enable_offset != ext_offset) {
> +            continue;
> +        }
> +
> +        return isa_edata_arr[i].min_version;
> +    }
> +
> +    g_assert_not_reached();
> +}
> +
> +static void cpu_cfg_ext_auto_update(RISCVCPU *cpu, uint32_t ext_offset,
> +                                    bool value)
> +{
> +    CPURISCVState *env = &cpu->env;
> +    bool prev_val = isa_ext_is_enabled(cpu, ext_offset);
> +    int min_version;
> +
> +    if (prev_val == value) {
> +        return;
> +    }
> +
> +    if (value && env->priv_ver != PRIV_VERSION_LATEST) {
> +        /* Do not enable it if priv_ver is older than min_version */
> +        min_version = cpu_cfg_ext_get_min_version(ext_offset);
> +        if (env->priv_ver < min_version) {
> +            return;
> +        }
> +    }
> +
> +    isa_ext_update_enabled(cpu, ext_offset, value);
> +}
> +
>  const char * const riscv_int_regnames[] = {
>      "x0/zero", "x1/ra",  "x2/sp",  "x3/gp",  "x4/tp",  "x5/t0",   "x6/t1",
>      "x7/t2",   "x8/s0",  "x9/s1",  "x10/a0", "x11/a1", "x12/a2",  "x13/a3",
> @@ -1268,12 +1305,12 @@ void riscv_cpu_validate_set_extensions(RISCVCPU *cpu, Error **errp)
>
>      /* zca, zcd and zcf has a PRIV 1.12.0 restriction */
>      if (riscv_has_ext(env, RVC) && env->priv_ver >= PRIV_VERSION_1_12_0) {
> -        cpu->cfg.ext_zca = true;
> +        cpu_cfg_ext_auto_update(cpu, CPU_CFG_OFFSET(ext_zca), true);
>          if (riscv_has_ext(env, RVF) && env->misa_mxl_max == MXL_RV32) {
> -            cpu->cfg.ext_zcf = true;
> +            cpu_cfg_ext_auto_update(cpu, CPU_CFG_OFFSET(ext_zcf), true);
>          }
>          if (riscv_has_ext(env, RVD)) {
> -            cpu->cfg.ext_zcd = true;
> +            cpu_cfg_ext_auto_update(cpu, CPU_CFG_OFFSET(ext_zcd), true);
>          }
>      }
>
> --
> 2.41.0
>
>