Re: [PATCH v6 04/14] riscv: sbi: add FWFT extension interface

[Atish Patra <atish.patra@linux.dev>]

On 4/24/25 10:31 AM, Clément Léger wrote:
> This SBI extensions enables supervisor mode to control feature that are
> under M-mode control (For instance, Svadu menvcfg ADUE bit, Ssdbltrp
> DTE, etc). Add an interface to set local features for a specific cpu
> mask as well as for the online cpu mask.
> 
> Signed-off-by: Clément Léger <cleger@rivosinc.com>
> Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
> ---
>   arch/riscv/include/asm/sbi.h | 17 +++++++++++
>   arch/riscv/kernel/sbi.c      | 57 ++++++++++++++++++++++++++++++++++++
>   2 files changed, 74 insertions(+)
> 
> diff --git a/arch/riscv/include/asm/sbi.h b/arch/riscv/include/asm/sbi.h
> index 7ec249fea880..3bbef56bcefc 100644
> --- a/arch/riscv/include/asm/sbi.h
> +++ b/arch/riscv/include/asm/sbi.h
> @@ -503,6 +503,23 @@ int sbi_remote_hfence_vvma_asid(const struct cpumask *cpu_mask,
>   				unsigned long asid);
>   long sbi_probe_extension(int ext);
>   
> +int sbi_fwft_set(u32 feature, unsigned long value, unsigned long flags);
> +int sbi_fwft_set_cpumask(const cpumask_t *mask, u32 feature,
> +			 unsigned long value, unsigned long flags);
> +/**
> + * sbi_fwft_set_online_cpus() - Set a feature on all online cpus
> + * @feature: The feature to be set
> + * @value: The feature value to be set
> + * @flags: FWFT feature set flags
> + *
> + * Return: 0 on success, appropriate linux error code otherwise.
> + */
> +static inline int sbi_fwft_set_online_cpus(u32 feature, unsigned long value,
> +					   unsigned long flags)
> +{
> +	return sbi_fwft_set_cpumask(cpu_online_mask, feature, value, flags);
> +}
> +
>   /* Check if current SBI specification version is 0.1 or not */
>   static inline int sbi_spec_is_0_1(void)
>   {
> diff --git a/arch/riscv/kernel/sbi.c b/arch/riscv/kernel/sbi.c
> index 1d44c35305a9..d57e4dae7dac 100644
> --- a/arch/riscv/kernel/sbi.c
> +++ b/arch/riscv/kernel/sbi.c
> @@ -299,6 +299,63 @@ static int __sbi_rfence_v02(int fid, const struct cpumask *cpu_mask,
>   	return 0;
>   }
>   
> +/**
> + * sbi_fwft_set() - Set a feature on the local hart
> + * @feature: The feature ID to be set
> + * @value: The feature value to be set
> + * @flags: FWFT feature set flags
> + *
> + * Return: 0 on success, appropriate linux error code otherwise.
> + */
> +int sbi_fwft_set(u32 feature, unsigned long value, unsigned long flags)
> +{
> +	return -EOPNOTSUPP;
> +}
> +
> +struct fwft_set_req {
> +	u32 feature;
> +	unsigned long value;
> +	unsigned long flags;
> +	atomic_t error;
> +};
> +
> +static void cpu_sbi_fwft_set(void *arg)
> +{
> +	struct fwft_set_req *req = arg;
> +	int ret;
> +
> +	ret = sbi_fwft_set(req->feature, req->value, req->flags);
> +	if (ret)
> +		atomic_set(&req->error, ret);

What happens when cpuX executed first reported an error but cpuY 
executed this function later and report success.

The error will be masked in that case.

> +}
> +
> +/**
> + * sbi_fwft_set_cpumask() - Set a feature for the specified cpumask
> + * @mask: CPU mask of cpus that need the feature to be set
> + * @feature: The feature ID to be set
> + * @value: The feature value to be set
> + * @flags: FWFT feature set flags
> + *
> + * Return: 0 on success, appropriate linux error code otherwise.
> + */
> +int sbi_fwft_set_cpumask(const cpumask_t *mask, u32 feature,
> +			       unsigned long value, unsigned long flags)
> +{
> +	struct fwft_set_req req = {
> +		.feature = feature,
> +		.value = value,
> +		.flags = flags,
> +		.error = ATOMIC_INIT(0),
> +	};
> +
> +	if (feature & SBI_FWFT_GLOBAL_FEATURE_BIT)
> +		return -EINVAL;
> +
> +	on_each_cpu_mask(mask, cpu_sbi_fwft_set, &req, 1);
> +
> +	return atomic_read(&req.error);
> +}
> +
>   /**
>    * sbi_set_timer() - Program the timer for next timer event.
>    * @stime_value: The value after which next timer event should fire.