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

[Jürgen Groß <jgross@xxxxxxxx>]

On 05.02.20 10:03, Dietmar Hahn wrote:
> 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"
Weird, there should be "early console in extract_kernel\n" before that.

> But not all of the text is seen!
Weird again - the address should be printed.

> 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.
But polling is synchronous (see serial_putchar() in
arch/x86/boot/compressed/misc.c). So a reboot indicates a very early
failure.

Can you please show the complete kdump kernel boot parameters?


Juergen

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