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

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Message-ID: <alpine.DEB.2.20.1611101125090.3501@nanos>
Date:   Thu, 10 Nov 2016 12:13:04 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "M. Vefa Bicakci" <m.v.b@...box.com>
cc:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        "Charles (Chas) Williams" <ciwillia@...cade.com>,
        "x86@...nel.org" <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        David Vrabel <david.vrabel@...rix.com>,
        Juergen Gross <jgross@...e.com>
Subject: Re: [PATCH] x86/cpuid: Deal with broken firmware once more

On Thu, 10 Nov 2016, M. Vefa Bicakci wrote:

> I have found that your patch unfortunately does not improve the situation
> for me. Here is an excerpt obtained from the dmesg of a kernel compiled
> with this patch *as well as* Sebastian's patch:

> [    0.002561] CPU: Physical Processor ID: 0
> [    0.002566] CPU: Processor Core ID: 0
> [    0.002572] [Firmware Bug]: CPU0: APIC id mismatch. Firmware: ffff CPUID: 2

So apic->cpu_present_to_apicid() gives us a completely bogus APIC id which
translates to a bogus package id. And looking at the XEN code:

   xen_pv_apic.cpu_present_to_apicid = xen_cpu_present_to_apicid,

and xen_cpu_present_to_apicid does:

static int xen_cpu_present_to_apicid(int cpu)
{
        if (cpu_present(cpu))
                return xen_get_apic_id(xen_apic_read(APIC_ID));
        else
                return BAD_APICID;
}

So independent of which present CPU we query we get just some random
information, in the above case we get BAD_APICID from xen_apic_read() not
from the else path as this CPU _IS_ present.

What's so wrong with storing the fricking firmware supplied APICid as
everybody else does and report it back when queried?

This damned attitude of we just hack the code into submission and let
everybody else deal with the outcoming is utterly annoying.

Thanks,

	tglx