Re: [PATCHv6 01/16] x86/cpu: Enumerate the LASS feature bits

Xin Li
2025-06-20T23:47:32Z

On 6/20/2025 10:31 AM, Kirill A. Shutemov wrote:
> On Fri, Jun 20, 2025 at 08:36:30AM -0700, Xin Li wrote:
>> On 6/20/2025 6:53 AM, Kirill A. Shutemov wrote:
>>> diff --git a/arch/x86/Kconfig.cpufeatures b/arch/x86/Kconfig.cpufeatures
>>> index 250c10627ab3..9574c198fc08 100644
>>> --- a/arch/x86/Kconfig.cpufeatures
>>> +++ b/arch/x86/Kconfig.cpufeatures
>>> @@ -124,6 +124,10 @@ config X86_DISABLED_FEATURE_PCID
>>> def_bool y
>>> depends on !X86_64
>>> +config X86_DISABLED_FEATURE_LASS
>>> + def_bool y
>>> + depends on !X86_64
>>> +
>>> config X86_DISABLED_FEATURE_PKU
>>> def_bool y
>>> depends on !X86_INTEL_MEMORY_PROTECTION_KEYS
>>
>> You don't need to add X86_DISABLED_FEATURE_LASS, because the LASS code
>> is NOT optional at build time, i.e., you now don't have CONFIG_X86_LASS.
>
> Hmm. But it is optional. It depends on CONFIG_X86_64. I don't think we
> want it to be advertised on 32-bit kernels.
>

I kind of ignore 32-bit...

But I simply hate adding a disabled feature that depends on !X86_64;
x86_64 has a broad scope, and new CPU features are often intentionally
not enabled for 32-bit.

(X86_DISABLED_FEATURE_PCID is the only one before LASS)