linux-kernel - Re: [PATCH v2] RISC-V: Enable cbo.clean/flush in usermode

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Message-ID: <20241224-2148923339996d2eed033b7e@orel>
Date: Tue, 24 Dec 2024 15:11:00 +0100
From: Andrew Jones <ajones@...tanamicro.com>
To: Yunhui Cui <cuiyunhui@...edance.com>
Cc: paul.walmsley@...ive.com, palmer@...belt.com, aou@...s.berkeley.edu, 
	conor@...nel.org, charlie@...osinc.com, samuel.holland@...ive.com, 
	cleger@...osinc.com, andybnac@...il.com, alexghiti@...osinc.com, 
	linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] RISC-V: Enable cbo.clean/flush in usermode

On Tue, Dec 24, 2024 at 08:39:46PM +0800, Yunhui Cui wrote:
> Enabling cbo.clean and cbo.flush in user mode makes it more
> convenient to manage the cache state and achieve better performance.
> 
> Signed-off-by: Yunhui Cui <cuiyunhui@...edance.com>
> ---
>  arch/riscv/kernel/cpufeature.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> index c0916ed318c2..60d180b98f52 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -30,6 +30,7 @@
>  #define NUM_ALPHA_EXTS ('z' - 'a' + 1)
>  
>  static bool any_cpu_has_zicboz;
> +static bool any_cpu_has_zicbom;
>  
>  unsigned long elf_hwcap __read_mostly;
>  
> @@ -87,6 +88,8 @@ static int riscv_ext_zicbom_validate(const struct riscv_isa_ext_data *data,
>  		pr_err("Zicbom disabled as cbom-block-size present, but is not a power-of-2\n");
>  		return -EINVAL;
>  	}
> +
> +	any_cpu_has_zicbom = true;
>  	return 0;
>  }
>  
> @@ -944,6 +947,11 @@ void __init riscv_user_isa_enable(void)
>  		current->thread.envcfg |= ENVCFG_CBZE;
>  	else if (any_cpu_has_zicboz)
>  		pr_warn("Zicboz disabled as it is unavailable on some harts\n");
> +
> +	if (riscv_has_extension_unlikely(RISCV_ISA_EXT_ZICBOM))
> +		current->thread.envcfg |= ENVCFG_CBCFE;
> +	else if (any_cpu_has_zicbom)
> +		pr_warn("Zicbom disabled as it is unavailable on some harts\n");
>  }
>  
>  #ifdef CONFIG_RISCV_ALTERNATIVE
> -- 
> 2.39.2
>

This looks good, so

Reviewed-by: Andrew Jones <ajones@...tanamicro.com>

but, as a separate patch, we should also provide hwprobe support like
zicboz has, i.e. add ZICBOM to the IMA ext0 key and add a key for the
zicbom block size. And then, as another patch, add a test_zicbom()
function to tools/testing/selftests/riscv/hwprobe/cbo.c.

Thanks,
drew