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

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Message-ID: <b5f6e797-580b-3c16-c89c-ec16cce084c5@oracle.com>
Date:   Thu, 10 Nov 2016 09:02:51 -0500
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        "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>,
        David Vrabel <david.vrabel@...rix.com>,
        Juergen Gross <jgross@...e.com>
Subject: Re: [PATCH] x86/cpuid: Deal with broken firmware once more

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.
How about returning cpu_data(cpu).initial_apicid?

And what was the original problem?

-boris

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