linux-kernel - Re: [v2 PATCH] arm64: mm: force write fault for atomic RMW instructions

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Date: Thu, 23 May 2024 18:07:08 +0100
From: Catalin Marinas <catalin.marinas@....com>
To: Yang Shi <yang@...amperecomputing.com>
Cc: will@...nel.org, anshuman.khandual@....com,
	scott@...amperecomputing.com, cl@...two.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [v2 PATCH] arm64: mm: force write fault for atomic RMW
 instructions

On Mon, May 20, 2024 at 09:56:36AM -0700, Yang Shi wrote:
> diff --git a/arch/arm64/include/asm/insn.h b/arch/arm64/include/asm/insn.h
> index db1aeacd4cd9..1cc73664fc55 100644
> --- a/arch/arm64/include/asm/insn.h
> +++ b/arch/arm64/include/asm/insn.h
> @@ -319,6 +319,7 @@ static __always_inline u32 aarch64_insn_get_##abbr##_value(void)	\
>   * "-" means "don't care"
>   */
>  __AARCH64_INSN_FUNCS(class_branch_sys,	0x1c000000, 0x14000000)
> +__AARCH64_INSN_FUNCS(class_atomic,	0x3b200c00, 0x38200000)

While this class includes all atomics that currently require write
permission, there's some unallocated space in this range and we don't
know what future architecture versions may introduce. Unfortunately we
need to check each individual atomic op in this class (not sure what the
overhead will be).

-- 
Catalin