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

[Dietmar Hahn <dietmar.hahn@xxxxxxxxxxxxxx>]

Am Dienstag, 4. Februar 2020, 15:18:53 CET schrieb Jürgen Groß:
> On 04.02.20 15:07, 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.
> 
> Which message?
> 
> Any chance you can build the kdump kernel with CONFIG_X86_VERBOSE_BOOTUP
> enabled?

Yes it's switched on. The Message is from the first debug message in
extract_kernel() - debug_putaddr(input_data):
"input_data: 0x"
But not all of the text is seen!
If I unterstand the early_serial_init code in 
arch/x86/boot/early_serial_console.c
correctly the serial line works with polling (no interrupts), so it seems the
reboot is initiated before the complete message is printed.

With an older SLES11SP4 system (xen-4.4.4 and linux-3.0.107) the kdump works.

Dietmar.

> 
> 
> Juergen




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