Re: [RFC v2 1/2] target/loongarch: Add loongson binary translation feature

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

Hi Bibo,

On 27/5/24 10:35, Bibo Mao wrote:
> Loongson Binary Translation (LBT) is used to accelerate binary
> translation, which contains 4 scratch registers (scr0 to scr3), x86/ARM
> eflags (eflags) and x87 fpu stack pointer (ftop).
> 
> Now LBT feature is added in kvm mode, not supported in TCG mode since
> it is not emulated. There are two feature flags such as forced_features
> and default_features for each vcpu, the real feature is still in cpucfg.
> Flag forced_features is parsed from command line, default_features is
> parsed from cpu type.
> 
> Flag forced_features has higher priority than flag default_features,
> default_features will be used if there is no command line option for LBT
> feature. If the feature is not supported with KVM host, it reports error
> and exits if forced_features is set, else it disables feature and continues
> if default_features is set.
> 
> Signed-off-by: Bibo Mao <maobibo@loongson.cn>
> ---
>   target/loongarch/cpu.c                | 69 +++++++++++++++++++++++++++
>   target/loongarch/cpu.h                | 12 +++++
>   target/loongarch/kvm/kvm.c            | 26 ++++++++++
>   target/loongarch/kvm/kvm_loongarch.h  | 16 +++++++
>   target/loongarch/loongarch-qmp-cmds.c |  2 +-
>   5 files changed, 124 insertions(+), 1 deletion(-)


> +static void loongarch_set_lbt(Object *obj, bool value, Error **errp)
> +{
> +    LoongArchCPU *cpu = LOONGARCH_CPU(obj);
> +
> +    if (!kvm_enabled()) {

Either set errp, ...

> +        return;
> +    }
> +
> +    if (value) {
> +        /* Enable binary translation for all architectures */
> +        cpu->env.forced_features |= BIT_ULL(LOONGARCH_FEATURE_LBT);
> +    } else {
> +        /* Disable default features also */
> +        cpu->env.default_features &= ~BIT_ULL(LOONGARCH_FEATURE_LBT);
> +    }
> +}
> +
>   void loongarch_cpu_post_init(Object *obj)
>   {
>       object_property_add_bool(obj, "lsx", loongarch_get_lsx,
>                                loongarch_set_lsx);
>       object_property_add_bool(obj, "lasx", loongarch_get_lasx,
>                                loongarch_set_lasx);

... or only add the property if KVM is enabled:

    if (kvm_enabled()) {

> +    object_property_add_bool(obj, "lbt", loongarch_get_lbt,
> +                             loongarch_set_lbt);
>   }