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

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Message-ID: <34456dc1-191f-dddb-7881-8409b654cdc8@oracle.com>
Date:   Thu, 10 Nov 2016 10:38:48 -0500
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Thomas Gleixner <tglx@...utronix.de>
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>,
        xen-devel <xen-devel@...ts.xen.org>
Subject: Re: [PATCH] x86/cpuid: Deal with broken firmware once more

On 11/10/2016 10:12 AM, Thomas Gleixner wrote:
> 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.

Unfortunately PV guests have neither. So we may need to emulate
something in xen_cpu_present_to_apicid().

-boris

(+xen-devel)