Re: Using kexec-crashdump with recent Xen and Linux HVM

[Vitaly Kuznetsov <vkuznets@redhat.com>]

Stefan Bader <stefan.bader@canonical.com> writes:

> After being asked about this I started to play around with Xen-4.4.1/4.5
> together with HVM Linux guest running 3.13/3.16/3.19. With mixed success.
> Usually rather failing.
>
> From a bit of research most activity to enable things were back in 2011. There
> was a bit of a throwback around Linux 3.2[1] but it appears [2] restored this in
> a backwards compatible way. Around 3.17 xen_nopv was introduced but I have not
> figured out a helpful usage of this.
>
> The failure exhibits no visible messages in the guest after the crash stacktrace
> caused by sysreq-trigger while 1vcpu seems to be in a spinning loop. On the host
> side I noticed changing messages (TX queue drain or EVCHNOP errors).
>
> Command-line is a mix of nomodeset (to keep cirrusdrm away) and some defaults
> from the kdump-tools (maxcpus=1 irqpoll nousb).
>
> The closest thing to success I can get to is using xen_emul_unplug=never for the
> normal boot (which propagates into the kexec command). This of course stops
> usage of the pv drivers. I also tried some variation of blacklisting the
> emulated drivers and using xen_emul_unplug=unnecessary but that did not seem to
> work for me. The crash-kexec boot without unplugging still fails to bring up the
> NIC but at least finds the root disk to store the dump there. But not using the
> pv drivers is not a setup one would want to have running just in case.
>
> So I was wondering whether I still miss something.

No, kexec/kdump for PVHVM has well-known issues. You can start reading
from http://lists.xen.org/archives/html/xen-devel/2014-12/msg01312.html
I'm still going to pick this up eventually.

>
> -Stefan
>
> [1] commit 12275dd4b747f5d87fa36229774d76bca8e63068
>     Revert "xen/pv-on-hvm kexec: add xs_reset_watches to shutdown watches..."
> [2] commit cb6b6df111e46b9d0f79eb971575fd50555f43f4
>     xen/pv-on-hvm kexec: add quirk for Xen 3.4 and shutdown watches.
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-- 
  Vitaly