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Re: Linux DomU freezes and dies under heavy memory shuffling

On 18.02.21 06:21, Roman Shaposhnik wrote:
On Wed, Feb 17, 2021 at 12:29 AM Jürgen Groß <jgross@xxxxxxxx <mailto:jgross@xxxxxxxx>> wrote:

    On 17.02.21 09:12, Roman Shaposhnik wrote:
     > Hi Jürgen, thanks for taking a look at this. A few comments below:
     > On Tue, Feb 16, 2021 at 10:47 PM Jürgen Groß <jgross@xxxxxxxx
    <mailto:jgross@xxxxxxxx>> wrote:
     >> On 16.02.21 21:34, Stefano Stabellini wrote:
     >>> + x86 maintainers
     >>> It looks like the tlbflush is getting stuck?
     >> I have seen this case multiple times on customer systems now, but
     >> reproducing it reliably seems to be very hard.
     > It is reliably reproducible under my workload but it take a long time
     > (~3 days of the workload running in the lab).

    This is by far the best reproduction rate I have seen up to now.

    The next best reproducer seems to be a huge installation with several
    hundred hosts and thousands of VMs with about 1 crash each week.

     >> I suspected fifo events to be blamed, but just yesterday I've been
     >> informed of another case with fifo events disabled in the guest.
     >> One common pattern seems to be that up to now I have seen this
     >> only on systems with Intel Gold cpus. Can it be confirmed to be true
     >> in this case, too?
     > I am pretty sure mine isn't -- I can get you full CPU specs if
    that's useful.

    Just the output of "grep model /proc/cpuinfo" should be enough.

processor: 3
vendor_id: GenuineIntel
cpu family: 6
model: 77
model name: Intel(R) Atom(TM) CPU  C2550  @ 2.40GHz
stepping: 8
microcode: 0x12d
cpu MHz: 1200.070
cache size: 1024 KB
physical id: 0
siblings: 4
core id: 3
cpu cores: 4
apicid: 6
initial apicid: 6
fpu: yes
fpu_exception: yes
cpuid level: 11
wp: yes
flags: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc cpuid aperfmperf pni pclmulqdq dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm sse4_1 sse4_2 movbe popcnt tsc_deadline_timer aes rdrand lahf_lm 3dnowprefetch cpuid_fault epb pti ibrs ibpb stibp tpr_shadow vnmi flexpriority ept vpid tsc_adjust smep erms dtherm ida arat md_clear vmx flags: vnmi preemption_timer invvpid ept_x_only flexpriority tsc_offset vtpr mtf vapic ept vpid unrestricted_guest
bugs: cpu_meltdown spectre_v1 spectre_v2 mds msbds_only
bogomips: 4800.19
clflush size: 64
cache_alignment: 64
address sizes: 36 bits physical, 48 bits virtual
power management:

     >> In case anybody has a reproducer (either in a guest or dom0) with a
     >> setup where a diagnostic kernel can be used, I'd be _very_
     > I can easily add things to Dom0 and DomU. Whether that will
    disrupt the
     > experiment is, of course, another matter. Still please let me
    know what
     > would be helpful to do.

    Is there a chance to switch to an upstream kernel in the guest? I'd like
    to add some diagnostic code to the kernel and creating the patches will
    be easier this way.

That's a bit tough -- the VM is based on stock Ubuntu and if I upgrade the kernel I'll have fiddle with a lot things to make workload functional again.

However, I can install debug kernel (from Ubuntu, etc. etc.)

Of course, if patching the kernel is the only way to make progress -- lets try that -- please let me know.

I have been able to gather some more data.

I have contacted the author of the upstream kernel patch I've been using
for our customer (and that helped, by the way).

It seems as if the problem is occurring when running as a guest at least
under Xen, KVM, and VMWare, and there have been reports of bare metal
cases, too. Hunting this bug is going on for several years now, the
patch author is at it since 8 months.

So we can rule out a Xen problem.

Finding the root cause is still important, of course, and your setup
seems to have the best reproduction rate up to now.

So any help would really be appreciated.

Is the VM self contained? Would it be possible to start it e.g. on a
test system on my side? If yes, would you be allowed to pass it on to


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