linux-kernel - Re: [PATCH v3 02/29] riscv: define default value for envcfg for task

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Date: Fri, 10 May 2024 15:33:36 -0700
From: Charlie Jenkins <charlie@...osinc.com>
To: Deepak Gupta <debug@...osinc.com>
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Subject: Re: [PATCH v3 02/29] riscv: define default value for envcfg for task

On Wed, Apr 03, 2024 at 04:34:50PM -0700, Deepak Gupta wrote:
> Defines a base default value for envcfg per task. By default all tasks
> should have cache zeroing capability. Any future base capabilities that
> apply to all tasks can be turned on same way.
> 
> Signed-off-by: Deepak Gupta <debug@...osinc.com>
> ---
>  arch/riscv/include/asm/csr.h | 2 ++
>  arch/riscv/kernel/process.c  | 6 ++++++
>  2 files changed, 8 insertions(+)
> 
> diff --git a/arch/riscv/include/asm/csr.h b/arch/riscv/include/asm/csr.h
> index 2468c55933cd..bbd2207adb39 100644
> --- a/arch/riscv/include/asm/csr.h
> +++ b/arch/riscv/include/asm/csr.h
> @@ -202,6 +202,8 @@
>  #define ENVCFG_CBIE_FLUSH		_AC(0x1, UL)
>  #define ENVCFG_CBIE_INV			_AC(0x3, UL)
>  #define ENVCFG_FIOM			_AC(0x1, UL)
> +/* by default all threads should be able to zero cache */
> +#define ENVCFG_BASE			ENVCFG_CBZE
>  
>  /* Smstateen bits */
>  #define SMSTATEEN0_AIA_IMSIC_SHIFT	58
> diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
> index 92922dbd5b5c..d3109557f951 100644
> --- a/arch/riscv/kernel/process.c
> +++ b/arch/riscv/kernel/process.c
> @@ -152,6 +152,12 @@ void start_thread(struct pt_regs *regs, unsigned long pc,
>  	else
>  		regs->status |= SR_UXL_64;
>  #endif
> +	/*
> +	 * read current envcfg settings, AND it with base settings applicable
> +	 * for all the tasks. Base settings should've been set up during CPU
> +	 * bring up.
> +	 */
> +	current->thread_info.envcfg = csr_read(CSR_ENVCFG) & ENVCFG_BASE;

This needs to be gated on xlinuxenvcfg.

- Charlie

>  }
>  
>  void flush_thread(void)
> -- 
> 2.43.2
>