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

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