linux-kernel - Re: [PATCH v2 1/3] x86/fred: Parse cmdline param "fred=" in cpu_parse_early

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Message-ID: <7fad52e6-83cf-4c17-9b3f-4dfa087f8fc4@zytor.com>
Date: Fri, 12 Jul 2024 10:40:48 -0700
From: Xin Li <xin@...or.com>
To: Nikolay Borisov <nik.borisov@...e.com>, linux-kernel@...r.kernel.org
Cc: hpa@...or.com, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, peterz@...radead.org,
        andrew.cooper3@...rix.com, houwenlong.hwl@...group.com
Subject: Re: [PATCH v2 1/3] x86/fred: Parse cmdline param "fred=" in
 cpu_parse_early_param()

On 7/10/2024 11:53 AM, Nikolay Borisov wrote:
> On 9.07.24 г. 18:40 ч., Xin Li (Intel) wrote:

>> @@ -1510,6 +1510,11 @@ static void __init cpu_parse_early_param(void)
>>       if (cmdline_find_option_bool(boot_command_line, "nousershstk"))
>>           setup_clear_cpu_cap(X86_FEATURE_USER_SHSTK);
>> +    /* Minimize the gap between FRED is available and available but 
>> disabled. */
>> +    arglen = cmdline_find_option(boot_command_line, "fred", arg, 
>> sizeof(arg));
>> +    if (arglen != 2 || strncmp(arg, "on", 2))
> 
> I'm confused why you keep perverting the calling convention of 
> cmdline_find_option. The doc clearly states:
> 
>      * Returns the position of that @option (starts counting with 1)
>      * or 0 on not found.  @option will only be found if it is found
>      * as an entire word in @cmdline.  For instance, if @option="car"
>      * then a cmdline which contains "cart" will not match.
> 
> You should only care if arglen is non 0, which if it is you check if its 
> value equal 'on', why bother with its starting position?
> 

Well, just look at how it is used in match_option() in
arch/x86/kernel/cpu/bugs.c and arch/x86/kernel/cpu/intel.c.

This is a short version and it will be expanded once we have more
option strings well defined (match_option() should be a common lib
function then).