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

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Date:   Sun, 13 Nov 2016 01:05:19 +0300
From:   "M. Vefa Bicakci" <m.v.b@...box.com>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.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>
Subject: Re: [PATCH] x86/cpuid: Deal with broken firmware once more

On 11/10/2016 06:31 PM, Boris Ostrovsky wrote:
> On 11/10/2016 10:05 AM, Charles (Chas) Williams wrote:
>>
>>
>> On 11/10/2016 09:02 AM, 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.
>>> How about returning cpu_data(cpu).initial_apicid?
>>>
>>> And what was the original problem?
>>
>> The original issue I found was that VMware was returning a different set
>> of APIC id's in the ACPI tables than what it advertised on the CPU's.
>>
>> http://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1266716.html
> 
> For Xen, we recently added a6a198bc60e6 ("xen/x86: Update topology map
> for PV VCPUs") to at least temporarily work around some topology map
> problems that PV guests have with RAPL (which I think is what Vefa's
> problem was).

Hello Boris,

(Sorry for the delay!)

It appears that the problem is a bit different compared to the one
corrected by a6a198bc60e6, because my kernel tree -- based on 4.8.6 --
already includes the -stable backport of that commit, i.e.
  88540ad0820ddfb05626e0136c0e5a79cea85fd1

The patch I included in my previous e-mail (dated 2016-11-10) corrects
root cause of the issue I am having with 4.8.6. Sebastian's original
patch adding error checking to the RAPL module prevents the RAPL module
from causing a kernel oops without my patch.

The issue I am experiencing is caused by the boot-up code in the
'init_apic_mappings' function switching the APIC ops structure from
Xen's structure to a no-op structure by calling the 'apic_disable'
function. Please let me know if I can clarify or elaborate.

For the record, using 4.8.7 without my correction patch patch does not
rectify the issue at hand. 4.8.7 changes the call site of the
'init_apic_mapping' function, so I had thought that it could be helpful.

Thank you,

Vefa