linux-kernel - Re: [PATCH v2 1/3] x86/cpufeatures: Add {required,disabled} feature configs

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Date: Sat, 22 Jun 2024 10:16:32 -0700
From: Xin Li <xin@...or.com>
To: Borislav Petkov <bp@...en8.de>
Cc: linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        tglx@...utronix.de, mingo@...hat.com, dave.hansen@...ux.intel.com,
        x86@...nel.org, hpa@...or.com, will@...nel.org, peterz@...radead.org,
        akpm@...ux-foundation.org, acme@...nel.org, namhyung@...nel.org
Subject: Re: [PATCH v2 1/3] x86/cpufeatures: Add {required,disabled} feature
 configs

On 6/21/2024 10:32 AM, Borislav Petkov wrote:
> On Sun, Jun 16, 2024 at 01:57:41AM -0700, Xin Li (Intel) wrote:
>> diff --git a/arch/x86/Kconfig.cpufeatures b/arch/x86/Kconfig.cpufeatures
>> new file mode 100644
>> index 000000000000..5ed24e45df87
>> --- /dev/null
>> +++ b/arch/x86/Kconfig.cpufeatures
>> @@ -0,0 +1,197 @@
>> +# SPDX-License-Identifier: GPL-2.0
>> +#
>> +# x86 feature bits (see arch/x86/include/asm/cpufeatures.h) that are
>> +# either REQUIRED to be enabled, or DISABLED (always ignored) for this
>> +# particular compile-time configuration.  The tests for these features
>> +# are turned into compile-time constants via the generated
>> +# <asm/featuremasks.h>.
>> +#
>> +# The naming of these variables *must* match asm/cpufeatures.h, e.g.,
>> +#     X86_FEATURE_ALWAYS <==> X86_REQUIRED_FEATURE_ALWAYS
>> +#     X86_FEATURE_FRED   <==> X86_DISABLED_FEATURE_FRED
>> +#
>> +# And these REQUIRED and DISABLED config options are manipulated in an
>> +# AWK script as the following example:
>> +#
>> +#                          +----------------------+
>> +#                          |    X86_FRED = y ?    |
>> +#                          +----------------------+
>> +#                              /             \
>> +#                           Y /               \ N
>> +#  +-------------------------------------+   +-------------------------------+
>> +#  | X86_DISABLED_FEATURE_FRED undefined |   | X86_DISABLED_FEATURE_FRED = y |
>> +#  +-------------------------------------+   +-------------------------------+
>> +#                                                        |
>> +#                                                        |
>> +#     +-------------------------------------------+      |
>> +#     | X86_FEATURE_FRED: feature word 12, bit 17 | ---->|
>> +#     +-------------------------------------------+      |
>> +#                                                        |
>> +#                                                        |
>> +#                                     +-------------------------------+
>> +#                                     | set bit 17 of DISABLED_MASK12 |
>> +#                                     +-------------------------------+
>> +#
> 
> Look ma, a picture. :-)
> 
> But yeah, this is better.
> 

We are better in intercepting pictures :)

Thanks!
     Xin