linux-kernel - Re: [PATCH v10 01/15] x86/cpu: Enumerate the LASS feature bits

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Message-ID: <7a5a28a3-baf4-4915-8585-eae8cd323895@zytor.com>
Date: Wed, 8 Oct 2025 07:16:28 +0800
From: Xin Li <xin@...or.com>
To: Sohil Mehta <sohil.mehta@...el.com>,
        "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>, "bp@...en8.de" <bp@...en8.de>,
        "x86@...nel.org" <x86@...nel.org>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>
Cc: "corbet@....net" <corbet@....net>, "ardb@...nel.org" <ardb@...nel.org>,
        "david.laight.linux@...il.com" <david.laight.linux@...il.com>,
        "luto@...nel.org" <luto@...nel.org>,
        "jpoimboe@...nel.org" <jpoimboe@...nel.org>,
        "andrew.cooper3@...rix.com" <andrew.cooper3@...rix.com>,
        "Luck, Tony" <tony.luck@...el.com>,
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        "geert@...ux-m68k.org" <geert@...ux-m68k.org>
Subject: Re: [PATCH v10 01/15] x86/cpu: Enumerate the LASS feature bits

On 10/8/2025 4:49 AM, Sohil Mehta wrote:
>>>   
>>> +config X86_DISABLED_FEATURE_LASS
>>> +	def_bool y
>>> +	depends on X86_32
>>> +
>> All the other ones in the file are !X86_64. Why do this one X86_32?
>>
> The double negation (DISABLED and !X86_64) was harder to follow when
> this was initially posted.
> 
> https://lore.kernel.org/lkml/73796800-819b-4433-b0ef-db852336d7a4@zytor.com/
> https://lore.kernel.org/lkml/756e93a2-7e42-4323-ae21- 
> a5437e71148e@...radead.org/
> 
> I don't have a strong preference. I guess the inconsistency makes it
> confusing as well. Will change it back to !X86_64 unless Xin objects.

I prefer to use X86_32, which is more direct.

Now the only disabled feature when !X86_64 is X86_DISABLED_FEATURE_PCID.
And I would expect the disabled features due to lack of 32-bit enabling 
will keep growing until we remove 32-bit kernel code.  I was also thinking
to move all such disabled features to a dedicated file when the total
reaches 3.  But hopefully removing 32-bit will happen first.