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

[Manoj Iyer]

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
============================