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

[Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>]

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.

Igor

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