Date: Fri, 18 Nov 2016 12:16:55 +0100 (CET)
From: Thomas Gleixner <tglx@linutronix.de>
To: Boris Ostrovsky <boris.ostrovsky@oracle.com>
cc: "M. Vefa Bicakci" <m.v.b@runbox.com>,
        "Charles (Chas) Williams" <ciwillia@Brocade.com>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        "x86@kernel.org" <x86@kernel.org>, LKML <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <peterz@infradead.org>, Borislav Petkov <bp@alien8.de>,
        David Vrabel <david.vrabel@citrix.com>,
        Juergen Gross <jgross@suse.com>, xen-devel <xen-devel@lists.xen.org>
Subject: Re: [PATCH] x86/cpuid: Deal with broken firmware once more
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On Mon, 14 Nov 2016, Boris Ostrovsky wrote:
> On 11/13/2016 06:42 PM, M. Vefa Bicakci wrote:
> 
> > I found out that my domU kernels invoke the 'apic_disable' function
> > because CONFIG_X86_MPPARSE was not enabled in my kernel configuration,
> > which would cause the 'smp_found_config' bit to be unset at boot-up.
> 
> smp_found_config is not the problem, it is usually zero for Xen PV guests.
> 
> What is the problem is that because of your particular config selection
> acpi_mps_check() fails (with the error message that you mention below) and
> that leads to X86_FEATURE_APIC being cleared. And then we indeed switch to
> APIC noop and things go south after that.

Indeed. And what really puzzles me is that Xen manages to bring up a
secondary CPU despite APIC being disabled. 

There are quite some assumptions about no APIC == no SMP in all of x86. Can
we please make Xen behave like anything else?

Thanks,

	tglx