linux-kernel - Re: [PATCH v2 01/10] x86/Kconfig: enable X86_X2APIC by default and improve help text

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Date:   Fri, 4 Nov 2022 10:29:33 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     "Elliott, Robert (Servers)" <elliott@....com>,
        Mateusz Jończyk <mat.jonczyk@...pl>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>, Yinghai Lu <yinghai@...nel.org>,
        Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH v2 01/10] x86/Kconfig: enable X86_X2APIC by default and
 improve help text

On 11/3/22 16:41, Elliott, Robert (Servers) wrote:
> How are the defconfig files supposed to keep up with valid
> combinations of options?

On some level, it doesn't matter as long as "make defconfig" and the
Kconfig rules result in something generally sane.

> Despite its filename, arch/x86/configs/x86_64_defconfig does not even have:
>   CONFIG_X86_64=y
> which enables many options. That was added by:
>   commit 622e3f28e50f ("x86: 64-bit defconfig remake")
>   Sun May 4 19:57:19 2008 +0400 
> but removed by:
>   commit 8b1bb90701f9a51f ("defconfig reduction")
>   Sat Aug 14 22:05:58 2010 +0200
> 
> It does have
>   CONFIG_SMP=y
> 
> which should imply X86_LOCAL_APIC, but that's missing too.
> 
> It does have 
>   CONFIG_HYPERVISOR_GUEST=y
> so doesn't need IRQ_REMAP to enable X86_X2APIC.

It sounds like folks generally want the defconfig files to have minimal
contents.  CONFIG_X86_64 isn't in there because it's not _needed_.

So, if the attached patch results in:

$ rm .config
$ make defconfig
$ grep X86_X2APIC .config
CONFIG_X86_X2APIC=y

Is there really anything else we need?  Kconfig seems to have figured
everything out just fine and without any complaints.
View attachment "x64-defconfig.patch" of type "text/x-patch" (411 bytes)