linux-kernel - Re: [PATCH 1/2] riscv: Correct the initialized flow of FP register

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Date:   Mon, 12 Aug 2019 07:58:16 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Vincent Chen <vincent.chen@...ive.com>
Cc:     paul.walmsley@...ive.com, palmer@...ive.com, aou@...s.berkeley.edu,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] riscv: Correct the initialized flow of FP register

> +static inline void fstate_off(struct task_struct *task,
> +			       struct pt_regs *regs)
> +{
> +	regs->sstatus = (regs->sstatus & ~(SR_FS)) | SR_FS_OFF;

No need for the inner braces here.

> +}
> +
>  static inline void fstate_save(struct task_struct *task,
>  			       struct pt_regs *regs)
>  {
> diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
> index f23794b..e3077ee 100644
> --- a/arch/riscv/kernel/process.c
> +++ b/arch/riscv/kernel/process.c
> @@ -64,8 +64,16 @@ void start_thread(struct pt_regs *regs, unsigned long pc,
>  	unsigned long sp)
>  {
>  	regs->sstatus = SR_SPIE;
> -	if (has_fpu)
> +	if (has_fpu) {
>  		regs->sstatus |= SR_FS_INITIAL;
> +#ifdef CONFIG_FPU
> +		/*
> +		 * Restore the initial value to the FP register
> +		 * before starting the user program.
> +		 */
> +		fstate_restore(current, regs);
> +#endif

fstate_restore has a no-op stub for the !CONFIG_FPU case, so the ifdef
here is not needed.

Otherwise this looks good to me:

Reviewed-by: Christoph Hellwig <hch@....de>