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

[Dietmar Hahn <dietmar.hahn@xxxxxxxxxxxxxx>]

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.
Thanks.
Dietmar.


> 
> Igor




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