Re: [PATCH] RISC-V: Enable Zicbom in usermode

From: Conor Dooley <conor@kernel.org>
To: Yunhui Cui <cuiyunhui@bytedance.com>
Cc: punit.agrawal@bytedance.com, paul.walmsley@sifive.com,
	palmer@dabbelt.com, aou@eecs.berkeley.edu, cleger@rivosinc.com,
	charlie@rivosinc.com, evan@rivosinc.com,
	samuel.holland@sifive.com, andybnac@gmail.com,
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] RISC-V: Enable Zicbom in usermode
Date: Fri, 25 Oct 2024 11:16:44 +0100	[thread overview]
Message-ID: <20241025-puritan-sank-b8a828ef5872@spud> (raw)
In-Reply-To: <20241025091527.57825-1-cuiyunhui@bytedance.com>

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On Fri, Oct 25, 2024 at 05:15:27PM +0800, Yunhui Cui wrote:
> Like Zicboz, by enabling the corresponding bits of senvcfg,
> the instructions cbo.clean, cbo.flush, and cbo.inval can be
> executed normally in user mode.
> 
> Signed-off-by: Yunhui Cui <cuiyunhui@bytedance.com>
> ---
>  arch/riscv/kernel/cpufeature.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> index 1992ea64786e..bc850518ab41 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -924,7 +924,7 @@ unsigned long riscv_get_elf_hwcap(void)
>  void __init riscv_user_isa_enable(void)
>  {
>  	if (riscv_has_extension_unlikely(RISCV_ISA_EXT_ZICBOZ))
> -		current->thread.envcfg |= ENVCFG_CBZE;
> +		current->thread.envcfg |= ENVCFG_CBIE | ENVCFG_CBCFE | ENVCFG_CBZE;

I believe we previously decided that userspace should not be allowed to
use zicbom, but that not withstanding - this is wrong. It should be
checking for Zicbom, not Zicboz.

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