linux-kernel - Re: [PATCH v2 3/4] arm64: introduce rodata=noalias

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Message-ID: <31d523f8-9160-44ba-86d9-e7dade2fa622@amperemail.onmicrosoft.com>
Date: Fri, 6 Dec 2024 13:50:55 +0800
From: Shijie Huang <shijie@...eremail.onmicrosoft.com>
To: Anshuman Khandual <anshuman.khandual@....com>,
 Huang Shijie <shijie@...amperecomputing.com>, catalin.marinas@....com,
 will@...nel.org
Cc: patches@...erecomputing.com, paulmck@...nel.org,
 akpm@...ux-foundation.org, thuth@...hat.com, rostedt@...dmis.org,
 xiongwei.song@...driver.com, ardb@...nel.org, steven.price@....com,
 suzuki.poulose@....com, mark.rutland@....com, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 cl@...amperecomputing.com
Subject: Re: [PATCH v2 3/4] arm64: introduce rodata=noalias


On 2024/12/6 12:29, Anshuman Khandual wrote:
>
> On 11/26/24 14:26, Huang Shijie wrote:
>> The rodata=noalias is the original rodata=on.
>>
>> The rodata=noalias can provide us more block mappings and contiguous hits
>> to map the linear region which minimize the TLB footprint. And the
>> linear aliases of pages belonging to read-only mappings in vmalloc
>> region are also marked as read-only.
>>
>> Also update kernel-parameters.txt for it:
>>     change "full" to "noalias"
>>
>> Signed-off-by: Huang Shijie <shijie@...amperecomputing.com>
>> ---
>>   Documentation/admin-guide/kernel-parameters.txt | 2 +-
>>   arch/arm64/include/asm/setup.h                  | 2 +-
>>   2 files changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
>> index dc663c0ca670..54b4df42e631 100644
>> --- a/Documentation/admin-guide/kernel-parameters.txt
>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>> @@ -5894,7 +5894,7 @@
>>   	rodata=		[KNL,EARLY]
>>   		on	Mark read-only kernel memory as read-only (default).
>>   		off	Leave read-only kernel memory writable for debugging.
>> -		full	Mark read-only kernel memory and aliases as read-only
>> +		noalias	Use more block mappings,may have better performance.
>>   		        [arm64]
>>   
>>   	rockchip.usb_uart
>> diff --git a/arch/arm64/include/asm/setup.h b/arch/arm64/include/asm/setup.h
>> index 5ded3bd11476..3d96dde4d214 100644
>> --- a/arch/arm64/include/asm/setup.h
>> +++ b/arch/arm64/include/asm/setup.h
>> @@ -31,7 +31,7 @@ static inline bool arch_parse_debug_rodata(char *arg)
>>   		return true;
>>   	}
>>   
>> -	if (!strcmp(arg, "full")) {
>> +	if (!strcmp(arg, "noalias")) {
>>   		rodata_enabled = true;
>>   		rodata_full = false;
>>   		return true;
> This patch should be folded back into [PATCH 1/4] ensuring that
Thanks, I will do it in next version.
>
> - "rodata=" processing gets updated completely i.e dropping 'full',
>    adding new 'noalias' and also updating the documentation at once
>
> - Avoids temporary the "full" option breakage as mentioned earlier
>
> Also please do add in code comment above arch_parse_debug_rodata()
> function explaining all the options after these update.

No problem.


Thanks

Huang Shijie