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Date: Thu, 23 May 2024 11:09:11 -0700 (PDT)
From: "Christoph Lameter (Ampere)" <cl@gentwo.org>
To: Catalin Marinas <catalin.marinas@arm.com>
cc: Yang Shi <yang@os.amperecomputing.com>, will@kernel.org, 
    anshuman.khandual@arm.com, scott@os.amperecomputing.com, 
    linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [v2 PATCH] arm64: mm: force write fault for atomic RMW
 instructions
In-Reply-To: <Zk93vBqAD3LgmbGb@arm.com>
Message-ID: <640f8606-2757-4e82-721f-9625d48ded65@gentwo.org>
References: <20240520165636.802268-1-yang@os.amperecomputing.com> <Zk93vBqAD3LgmbGb@arm.com>
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On Thu, 23 May 2024, Catalin Marinas wrote:

> 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).

Can you tell us which bits or pattern is not allocated? Maybe we can 
exclude that from the pattern.