linux-kernel - Re: [PATCH] x86/apic: Don't disable x2APIC if locked

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Message-ID: <c0e46d84-5015-34b4-a80b-758562118bde@intel.com>
Date:   Wed, 10 Aug 2022 14:57:19 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Daniel Sneddon <daniel.sneddon@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "Shutemov, Kirill" <kirill.shutemov@...el.com>
Cc:     "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
        "Gomez Iglesias, Antonio" <antonio.gomez.iglesias@...el.com>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
Subject: Re: [PATCH] x86/apic: Don't disable x2APIC if locked

On 8/10/22 13:29, Daniel Sneddon wrote:
> On 8/10/22 13:06, Daniel Sneddon wrote:
>> I could add a blurb to the
>> documentation where nox2apic is defined as a parameter as well.  
> While I'm at it, I'm thinking of adding something where CONFIG_X86_X2APIC is
> defined in kconfig.  I'll put in a blurb about selecting N on SPR systems could
> prevent you from booting due to the lock.

Please don't make it _too_ specific.  This is, after all, new
architecture that is presumably going to be in place long after we all
forget what SPR is.

Good Kconfig text would probably be something along the lines of:

	Some ~2022 and later systems are locked into x2APIC mode and can
	not fall back to the legacy APIC modes.  They will be unable to
	boot without enabling this option.

Would anybody hate if we just removed the CONFIG_X86_X2APIC prompt entirely?