Re: [PATCH v8 05/19] target/riscv/tcg: update priv_ver on user_set extensions

[Andrew Jones]

On Wed, Nov 01, 2023 at 05:41:50PM -0300, Daniel Henrique Barboza wrote:
> We'll add a new bare CPU type that won't have any default priv_ver. This
> means that the CPU will default to priv_ver = 0, i.e. 1.10.0.
> 
> At the same we'll allow these CPUs to enable extensions at will, but
> then, if the extension has a priv_ver newer than 1.10, we'll end up
> disabling it. Users will then need to manually set priv_ver to something
> other than 1.10 to enable the extensions they want, which is not ideal.
> 
> Change the setter() of multi letter extensions to allow user enabled
> extensions to bump the priv_ver of the CPU. This will make it
> conveniente for users to enable extensions for CPUs that doesn't set a
> default priv_ver.
> 
> This change does not affect any existing CPU: vendor CPUs does not allow
> extensions to be enabled, and generic CPUs are already set to priv_ver
> LATEST.
> 
> Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
> ---
>  target/riscv/tcg/tcg-cpu.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/target/riscv/tcg/tcg-cpu.c b/target/riscv/tcg/tcg-cpu.c
> index f54069d06f..b88fce98a4 100644
> --- a/target/riscv/tcg/tcg-cpu.c
> +++ b/target/riscv/tcg/tcg-cpu.c
> @@ -114,6 +114,22 @@ static int cpu_cfg_ext_get_min_version(uint32_t 
> ext_offset)
>      g_assert_not_reached();
>  }
>  
> +static void cpu_validate_multi_ext_priv_ver(CPURISCVState *env,
> +                                            uint32_t ext_offset)
> +{
> +    int ext_priv_ver;
> +
> +    if (env->priv_ver == PRIV_VERSION_LATEST) {
> +        return;
> +    }
> +
> +    ext_priv_ver = cpu_cfg_ext_get_min_version(ext_offset);
> +
> +    if (env->priv_ver < ext_priv_ver) {
> +        env->priv_ver = ext_priv_ver;
> +    }

This will ignore user input. If the user, for example, does

 -cpu rv64,priv_spec=v1.10.0,zicbom=on

then, afaict, priv_spec will be silently bumped to 1.12. I think we should
error out in that case instead. And, we should also error out for

 -cpu rv64,zicbom=on,priv_spec=v1.10.0

which means we should know when priv_spec is either

 - its default value
 - has been bumped by an extension
 - has been explicitly set by the user

> +}
> +
>  static void cpu_cfg_ext_auto_update(RISCVCPU *cpu, uint32_t ext_offset,
>                                      bool value)
>  {
> @@ -829,6 +845,10 @@ static void cpu_set_multi_ext_cfg(Object *obj, Visitor 
> *v, const char *name,
>          return;
>      }
>  
> +    if (value) {
> +        cpu_validate_multi_ext_priv_ver(&cpu->env, multi_ext_cfg->offset);
> +    }

Some misa extensions also have priv spec version dependencies. See
riscv_cpu_validate_misa_priv()

> +
>      isa_ext_update_enabled(cpu, multi_ext_cfg->offset, value);
>  }
>  
> -- 
> 2.41.0
>

Thanks,
drew