[3/3] arm64: Add software workaround for Falkor erratum 1041

[Manoj Iyer]

On Fri, 10 Nov 2017, Manoj Iyer wrote:

> On Thu, 9 Nov 2017, Manoj Iyer wrote:
>
>> 
>> James,
>> 
>> Looks like my VM test raised a false alarm. I retested stock Artful 4.13 
>> kernel (No erratum 1041 patches applied).
>> 
>
> James, an update on the crash (false alarm). We suspect this is a firmware 
> crash due to a possible fw bug. Once this is addressed I will be able to send 
> you the test results you requested on VM start/stop with the erratum 1041 
> patches applied.
>

James/Shanker,

I can report that VM start/stop/restart tests worked with the patches 
applied to Ubuntu 4.13 (Artful) kernel on the qdf2400 hardware.

Host: Ubuntu 4.13 with Erratum 1041 patches applied
Guest: Stock Ubuntu 4.13 kernel

- create 20 vms one at a time

10 iteration of:
- Stop (virsh destroy) 20 VMs one at a time
- Start (virsh start) 20 VMs one at a time.

Tested-by: Manoj Iyer <manoj.iyer at canonical.com>

>
>> Host: Ubuntu Artful 4.13 kernel with *no* erratum 1041 patches applied.
>> Guest: Ubuntu Zesty (4.10) kernel.
>> 
>> - Created 20 VMs one at a time
>> 
>> In a loop:
>> - Stop (virsh destroy) 20 VMs one at a time
>> - Start (virsh start) 20 VMs one at a time.
>> 
>> And, I am able to reproduce the system reset issue I previously reported. I 
>> think the problem I reported with VMs might have nothing to do with the 
>> erratum 1041 patches, and probably needs to be root caused seperately.
>> 
>> With stock 4.13 kernel (no erratum 1041 patches applied):
>> 
>> awrep6 login: [  461.881379] ACPI CPPC: PCC check channel failed. Status=0
>> [  462.051194] ACPI CPPC: PCC check channel failed. Status=0
>> [  462.223137] ACPI CPPC: PCC check channel failed. Status=0
>> [  462.633790] ACPI CPPC: PCC check channel failed. Status=0
>> [  463.231971] ACPI CPPC: PCC check channel failed. Status=0
>> [  463.403163] ACPI CPPC: PCC check channel failed. Status=0
>> [  463.822936] ACPI CPPC: PCC check channel failed. Status=0
>> [  463.995222] ACPI CPPC: PCC check channel failed. Status=0
>> [  464.130962] ACPI CPPC: PCC check channel failed. Status=0
>> [  464.258973] ACPI CPPC: PCC check channel failed. Status=0
>> [  465.283028] ACPI CPPC: PCC check channel failed. Status=0
>> 
>> 
>> SYS_DBG: Running SDI image (immediate mode)
>> SYS_DBG: Ram Dump Init
>> SYS_DBG: Failed to init SD card
>> SYS_DBG: Resetting system!
>> 
>> 
>> On Thu, 9 Nov 2017, Manoj Iyer wrote:
>> 
>>> 
>>> 
>>> 
>>> On Thu, 9 Nov 2017, Manoj Iyer wrote:
>>> 
>>>> 
>>>> James,
>>>> 
>>>> (sorry for top-posting)
>>>> 
>>>> Applied patch 3 patches to Ubuntu Artful Kernel ( 4.13.0-16-generic )
>>>> 
>>>> - Start 20 VMs one at a time
>>>> 
>>>> In a loop:
>>>> - Stop (virsh destroy) 20 VMs one at a time
>>>> - Start (virsh start) 20 VMs one at a time.
>>> 
>>> Fixing some confusion I might have introduced in my prev email.
>>> 
>>> - Applied all 3 patches to Ubuntu Artful Kernel ( 4.13.0-16-generic )
>>> 
>>> - Created 20 VMs one at a time
>>> 
>>> In a loop:
>>> - Stop (virsh destroy) 20 VMs one at a time
>>> - Start (virsh start) 20 VMs one at a time.
>>> 
>>>> 
>>>> The system reset's itself after starting the last VM on the 1st loop 
>>>> displaying the following:
>>>> 
>>>> awrep6 login: [ 603.349141] ACPI CPPC: PCC check channel failed. Status=0
>>>> [ 603.765101] ACPI CPPC: PCC check channel failed. Status=0
>>>> [ 603.937389] ACPI CPPC: PCC check channel failed. Status=0
>>>> [ 608.285495] ACPI CPPC: PCC check channel failed. Status=0
>>>> [ 608.289481] ACPI CPPC: PCC check channel failed. Status=0
>>>> 
>>>> SYS_DBG: Running SDI image (immediate mode)
>>>> SYS_DBG: Ram Dump Init
>>>> SYS_DBG: Failed to init SD card
>>>> SYS_DBG: Resetting system!
>>>> 
>>>> Followed by the following messages on system reboot:
>>>> [ 6.616891] BERT: Error records from previous boot:
>>>> [ 6.621655] [Hardware Error]: event severity: fatal
>>>> [ 6.626516] [Hardware Error]: imprecise tstamp: 0000-00-00 00:00:00
>>>> [ 6.632851] [Hardware Error]: Error 0, type: fatal
>>>> [ 6.637713] [Hardware Error]: section type: unknown, 
>>>> d2e2621c-f936-468d-0d84-15a4ed015c8b
>>>> [ 6.646045] [Hardware Error]: section length: 0x238
>>>> [ 6.651082] [Hardware Error]: 00000000: 72724502 5220726f 6f736165 
>>>> 6e55206e .Error Reason Un
>>>> [ 6.659761] [Hardware Error]: 00000010: 776f6e6b 0000006e 00000000 
>>>> 00000000 known...........
>>>> [ 6.668442] [Hardware Error]: 00000020: 00000000 00000000 00000000 
>>>> 00000000 ................
>>>> [ 6.677122] [Hardware Error]: 00000030: 00000000 00000000 00000000 
>>>> 00000000 ................
>>>> 
>>>> 
>>>> On Thu, 9 Nov 2017, James Morse wrote:
>>>> 
>>>>> Hi Manoj,
>>>>> 
>>>>> On 08/11/17 19:05, Manoj Iyer wrote:
>>>>>> On Thu, 2 Nov 2017, Shanker Donthineni wrote:
>>>>>>> The ARM architecture defines the memory locations that are permitted
>>>>>>> to be accessed as the result of a speculative instruction fetch from
>>>>>>> an exception level for which all stages of translation are disabled.
>>>>>>> Specifically, the core is permitted to speculatively fetch from the
>>>>>>> 4KB region containing the current program counter and next 4KB.
>>>>>>> 
>>>>>>> When translation is changed from enabled to disabled for the running
>>>>>>> exception level (SCTLR_ELn[M] changed from a value of 1 to 0), the
>>>>>>> Falkor core may errantly speculatively access memory locations outside
>>>>>>> of the 4KB region permitted by the architecture. The errant memory
>>>>>>> access may lead to one of the following unexpected behaviors.
>>>>> 
>>>>>> I applied the 3 patches to Ubuntu 4.13.0-16-generic (Artful) kernel and
>>>>>> ran stress-ng cpu tests on QDF2400 server
>>>>> 
>>>>> [...]
>>>>> 
>>>>>> Where stress-ng would spawn N workers and test cpu offline/online, 
>>>>>> perform
>>>>>> matrix operations, do rapid context switchs, and anonymous mmaps. 
>>>>>> Although
>>>>>> I was not able to reproduce the erratum on the stock 4.13 kernel using 
>>>>>> the
>>>>>> same test case, the patched kernel did not seem to introduce any
>>>>>> regressions either. I ran the stress-ng tests for over 8hrs found the
>>>>>> system to be stable.
>>>>> 
>>>>> 
>>>>> Could you throw kexec and KVM into the mix? This issue only shows up 
>>>>> when we
>>>>> disable the MMU, which we almost never do.
>>>>> 
>>>>> For CPU offline/online we make the PSCI 'offline' call with the MMU 
>>>>> enabled.
>>>>> When the CPU comes back firmware has reset the EL2/EL1 SCTLR from a 
>>>>> higher
>>>>> exception level, so it won't hit this issue.
>>>>> 
>>>>> One place we do this is kexec, where we drop into purgatory with the MMU 
>>>>> disabled.
>>>>> 
>>>>> The other is KVM unloading itself to return to the hyp stub. You can 
>>>>> stress this
>>>>> by starting and stopping a VM. When the number of VMs reaches 0 KVM 
>>>>> should
>>>>> unload via 'kvm_arch_hardware_disable()'.
>>>>> 
>>>>> 
>>>>> Thanks,
>>>>> 
>>>>> James
>>>>> 
>>>>> 
>>>> 
>>>> --
>>>> ============================
>>>> Manoj Iyer
>>>> Ubuntu/Canonical
>>>> ARM Servers - Cloud
>>>> ============================
>>>> 
>>>> 
>>> 
>>> --
>>> ============================
>>> Manoj Iyer
>>> Ubuntu/Canonical
>>> ARM Servers - Cloud
>>> ============================
>>> 
>>> 
>> 
>> --
>> ============================
>> Manoj Iyer
>> Ubuntu/Canonical
>> ARM Servers - Cloud
>> ============================
>> 
>> 
>
> --
> ============================
> Manoj Iyer
> Ubuntu/Canonical
> ARM Servers - Cloud
> ============================
>
>