Re: [Xen-devel] Kdump doesn't work when running with xen on newer hardware

[Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>]

On 04/02/2020 14:07, Dietmar Hahn wrote:
> Am Freitag, 31. Januar 2020, 22:59:19 CET schrieb Igor Druzhinin:
>> On 30/01/2020 13:03, Dietmar Hahn wrote:
>>> Hi,
>>>
>>> we use SLES12 with kernel-default-4.12.14-95.45.1.x86_64 and 
>>> xen-4.11.3_02-2.20.1.x86_64
>>>
>>> The dump kernel doesn't start after "echo c > /proc/sysrq_trigger".
>>> Last messages on console are:
>>> [  385.717532] Kernel panic - not syncing: Fatal exception
>>> [  385.734565] Kernel Offset: disabled
>>> (XEN) Hardware Dom0 crashed: Executing kexec image on cpu58
>>> (XEN) Shot down all CPUs
>>>
>>> After a short time a reboot is initiated.
>>> Without xen the kdump works.
>>>
>>> We see this behaviour only on newer hardware, for example a server with
>>> Intel(R) Xeon(R) Gold 6242 CPU @ 2.80GHz
>>>
>>> I built the fresh released xen-4.13 myself and tried it but this doesn't 
>>> help.
>>>
>>> I tried x2apic=off on the xen side and nox2apic on the linux side but no 
>>> success.
>>
>> Starting from Xen 4.12 we keep IOMMU enabled during kexec transition
>> which resolved the problem you're describing. But you also need to make
>> sure IOMMU is enabled in your kexec kernel (which I think is now the
>> default for most distros). You can still try to workaround the issue
>> you're seeing on 4.11 by using "iommu=dom0-passthough" Xen option.
> 
> I added "iommu=dom0-passthrough" to the xen-4.11 command line but no success.
> Further I added earlyprintk=... to the the kdump kernel and I could see the
> dump kernel started and only one message from extract_kernel()
> was printed. Then the reboot followed.
> 
> Because I'm not that familiar with this part of I would appreciate hints where
> to dig deeper.

Could you try to disable IOMMU completely in diagnostic purposes:
"iommu=off x2apic=off"? If that helps - it's still the same issue I'm
referring to. Could you post your current Xen cmdline?

Igor


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