Date:   Thu, 5 Jan 2017 22:05:39 +0800
From:   Daniel J Blueman <daniel@...ra.org>
To:     "Raj, Ashok" <ashok.raj@...el.com>, Borislav Petkov <bp@...e.de>,
        Paul Menzel <pmenzel@...gen.mpg.de>, tony.luck@...el.com,
        linux@...mhuis.info, len.brown@...el.com,
        Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: Dell XPS13: MCE (Hardware Error) reported

On 5 January 2017 at 13:00, Daniel J Blueman <daniel@...ra.org> wrote:
> On Thursday, January 5, 2017 at 9:20:04 AM UTC+8, Raj, Ashok wrote:
>> Hi Boris
>>
>> thanks for forwarding.
>>
>> > > CPUID Vendor Intel Family 6 Model 142
>> This is Kabylake Mobile
>>
>> > > Hardware event. This is not a software error.
>> > > MCE 1
>> > > CPU 0 BANK 7
>> > > MISC 7880018086 ADDR fef1ce40
>> > > TIME 1483543069 Wed Jan  4 16:17:49 2017
>> > > MCG status:
>> > > MCi status:
>> > > Error overflow
>> > > Uncorrected error
>> > > MCi_MISC register valid
>> > > MCi_ADDR register valid
>> > > Processor context corrupt
>> > > MCA: corrected filtering (some unreported errors in same region)
>> > > Generic CACHE Level-2 Generic Error
>> > > STATUS ee0000000040110a MCGSTATUS 0
>>
>> Decoding the bits further from MCi_STATUS above:
>> Val=1, OVER=1, UC=1, but EN=0 indicates this isn't a MCE, hence should have
>> been signaled by a CMCI.
>>
>> PCC=1, but should be ignored when EN=0.
>> MCACOD: 110a MSCOD: 0040
>>
>> If the system is stable enough after the report, can you send the output of
>> /proc/interrupts to confirm that.
>>
>> Although its reported as a L2 error, some memory errors can also manifest
>> itself as a cache error in certain cases.  In this case it looks like
>> some speculative fetch from bad memory might be the cause.
>>
>> > > MCGCAP c08 APICID 0 SOCKETID 0
>>
>> MCG_CAP: c08
>> Support CMCI(bit 10) - Corrected Machine Check Interrupt (CMCI_P) and
>> Threshold based error reporting (bit 11) (TES_P).
>>
>>
>> Do you have another machine which doesn't report these errors? if so try
>> swapping memory between them to see if the error disappears.
>>
>> I don't have the model specific error handy.. will check that in the meantime
>> to get some decoding as well.
>>
>> If you haven't already running some memory tests would also help.
>>
>> If you replaced the motherboard, did that involve both cpu and memory?
>> or just the motheboard swap?
>
> I see the MCE on my XPS 9360 also. It's not related to DRAM, as the
> physical address is in the non-coherent low MMIO window:
> MISC 7880018086 ADDR fef1ce40
>
> Which is declared as device memory:
> [    0.000000] PM: Registered nosave memory: [mem 0xfee01000-0xfeffffff]
>
> For core-generated cycles, it is between the local APIC space at
> FEE00000:FEEFFFF and SPI BIOS at FFE00000:FFFFFFFF, so will be
> subtractively decoded to the PCH, maybe being aborted due to a device
> not being enabled (hello TPM3 or new image processor).
>
> As it is logged as soon as the MCE driver initialises, it was probably
> logged during BIOS init, so there's not much we can do about it
> anyways.

That said, I have seen this reoccur after boot; there were no other
kernel messages around 300s uptime, and it hasn't occurred in the last
hours since:

$ dmesg | grep Machine
[    0.039072] mce: [Hardware Error]: Machine check events logged
[  300.069176] mce: [Hardware Error]: Machine check events logged

As I don't see a driver controlling this area of address space, the
access is likely initiated from the UEFI BIOS System Management Mode
handler, and we see the same pair of registers FEF1FF40, FEF1CE40
accessed each time.

Dan
-- 
Daniel J Blueman

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