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

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Date:   Thu, 3 Nov 2022 23:41:56 +0000
From:   "Elliott, Robert (Servers)" <elliott@....com>
To:     Dave Hansen <dave.hansen@...el.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



> -----Original Message-----
> From: Dave Hansen <dave.hansen@...el.com>
> Sent: Thursday, October 27, 2022 10:08 AM
...
> Subject: Re: [PATCH v2 01/10] x86/Kconfig: enable X86_X2APIC by default
> and improve help text
> 
> On 10/27/22 07:45, Elliott, Robert (Servers) wrote:
> >>  config X86_X2APIC
> >> -	bool "Support x2apic"
> >> +	bool "x2APIC interrupt controller architecture support"
> >>  	depends on X86_LOCAL_APIC && X86_64 && (IRQ_REMAP ||
> >> HYPERVISOR_GUEST)
> >> +	default y
> > Could this option be added to
> > 	arch/x86/configs/x86_64_defconfig
> >
> > so defconfig builds don't crash on current platforms?
> 
> Sounds reasonable.  Care to send a patch?

How are the defconfig files supposed to keep up with valid
combinations of options?

arch/x86/Kconfig has this set of dependencies:
  config X86_X2APIC
        bool "Support x2apic"
        depends on X86_LOCAL_APIC && X86_64 && (IRQ_REMAP || HYPERVISOR_GUEST)

  config X86_LOCAL_APIC
        def_bool y
        depends on X86_64 || SMP || X86_32_NON_STANDARD || X86_UP_APIC || PCI_MSI
        select IRQ_DOMAIN_HIERARCHY
        select PCI_MSI_IRQ_DOMAIN if PCI_MSI

  config X86_IO_APIC
        def_bool y
        depends on X86_LOCAL_APIC || X86_UP_IOAPIC

drivers/iommu/Kconfig has:
  config IRQ_REMAP
        bool "Support for Interrupt Remapping"
        depends on X86_64 && X86_IO_APIC && PCI_MSI && ACPI
        select DMAR_TABLE

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.