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

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Message-ID: <alpine.DEB.2.20.1611101610230.3501@nanos>
Date:   Thu, 10 Nov 2016 16:12:13 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>
cc:     "M. Vefa Bicakci" <m.v.b@...box.com>,
        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>,
        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, Boris Ostrovsky wrote:
> On 11/10/2016 06:13 AM, Thomas Gleixner wrote:
> > 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?
> 
> By firmware you mean ACPI? It is most likely not available to PV guests.

You either have to provide ACPI or MP tables. And either of those has to
provide the intial APIC ids for the CPUs. They are supposed to match the
IDs which are in the CPUID leafs.

> How about returning cpu_data(cpu).initial_apicid?

For a not yet brought up CPU. That's what the initial ACPI/MP table
enumeration is for.

Thanks,

	tglx