[v7, 01/10] riscv: Add support for kernel mode vector

[Eric Biggers]

On Thu, Dec 21, 2023 at 01:43:08PM +0000, Andy Chiu wrote:
> +/*
> + * We use a flag to track in-kernel Vector context. Currently the flag has the
> + * following meaning:
> + *
> + *  - bit 0-7 indicates whether the in-kernel Vector context is active. The
> + *    activation of this state disables the preemption. On a non-RT kernel, it
> + *    also disable bh. Currently only 0 and 1 are valid value for this field.
> + *    Other values are reserved for future uses.
> + */
> +
> +#define RISCV_KERNEL_MODE_V_MASK	0xff
> +
> +#define RISCV_KERNEL_MODE_V	0x1

Is there a reason this isn't just a single bit flag?

> +static inline void riscv_v_ctx_cnt_add(u32 offset)
> +{
> +	current->thread.riscv_v_flags += offset;
> +	barrier();
> +}
> +
> +static inline void riscv_v_ctx_cnt_sub(u32 offset)
> +{
> +	barrier();
> +	current->thread.riscv_v_flags -= offset;
> +}

What is the purpose of the barriers above?

> +static inline u32 riscv_v_ctx_cnt(void)
> +{
> +	return READ_ONCE(current->thread.riscv_v_flags);
> +}

What is the purpose of using READ_ONCE() here?

> diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
> index 4f21d970a129..5c4dcf518684 100644
> --- a/arch/riscv/kernel/process.c
> +++ b/arch/riscv/kernel/process.c
> @@ -187,7 +187,6 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
>  	*dst = *src;
>  	/* clear entire V context, including datap for a new task */
>  	memset(&dst->thread.vstate, 0, sizeof(struct __riscv_v_ext_state));
> -
>  	return 0;
>  }

Unnecessary whitespace change.

Otherwise this patch looks good, thanks!

- Eric