linux-kernel - Re: [PATCH] x86/cpuid: Deal with broken firmware once more

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Date:   Mon, 14 Nov 2016 20:21:22 -0500
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     "M. Vefa Bicakci" <m.v.b@...box.com>
Cc:     "Charles (Chas) Williams" <ciwillia@...cade.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        "x86@...nel.org" <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>,
        David Vrabel <david.vrabel@...rix.com>,
        Juergen Gross <jgross@...e.com>,
        xen-devel <xen-devel@...ts.xen.org>
Subject: Re: [PATCH] x86/cpuid: Deal with broken firmware once more



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.

-boris

>
> This would cause 'init_apic_mappings' to call 'apic_disable', which
> would cause Xen's 'apic' ops structure pointer to be replaced with the
> no-op APIC ops structure's pointer.
>
> The use of the no-op APIC ops structure would in turn cause invalid
> virtual CPU package identifiers to be generated. Invalid CPU package
> identifiers would in turn cause the RAPL module to produce a kernel oops
> due to potentially missing error handling.
>
> It looks like I have been ignoring the following kernel warning which I
> should have noticed a long time ago:
>
>   MPS support code is not built-in.
>   Using acpi=off or acpi=noirq or pci=noacpi may have problem
>
> To all on this e-mail thread, I learned a bit through this exercise, but
> I have also taken a lot of everyone's time and created quite a bit of
> e-mail traffic because of a kernel configuration issue on my end.
>
> My apologies.
>
> Vefa
>