Re: kexec and kdump on Xen??

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 17/04/14 02:19, Zhang, Yang Z wrote:
>
>>> Here is my environment:
>>> Xen version: latest Xen
>>> Xen boot command:
>>> 	kernel (hd0,0)/boot/xen.gz dom0_mem=4096M loglvl=all
>>> guest_loglvl=all
>> conring_size=4M crashkernel=128M@64M
>>>     module (hd0,0)/boot/vmlinuz-xen o
>> root=UUID=03a5e7c4-b8d0-45b4-a090-c34b06821cea pci=noaer max_loop=64
>> 3 debug
>>>     module (hd0,0)/boot/initrd-xen.img kexec version with Xen enabled:
>>> kexec-tools 2.0.6 released 18 April 2014
>>>
>>> Also, it shows error when trying to kexec (Xen -> Xen) ./kexec -l
>>> /boot/xen.gz Segmentation fault (core dumped)
>> We were focusing more on kdump than on other scenarios.
>> I suppose that kexec-tools assume that this compressed ELF file is
>> Linux Kernel and tries load it as usual which of course is completely
>> wrong. You should load Xen with at least "-t multiboot-x86" argument (read help printed by kexec).
>> However, I am not sure that this loader is actively maintained and works.
>>
>> Daniel
> Thanks for your comments.
>
> After investigation, I found some bugs (One is the segment overlap check failure and another one is related to x2apic). With some workarounds, now I am able to kexec from Xen into Linux.
> But it still fails to run kdump(Xen->linux). I add some debug messages in the key code path. It shows kexec_reloc() will cause machine reboot. Is it a known issue?
>
> BTW: Have you ever tried kdump(Xen->linux) successfully? If yes, can you share some BKMs? Thanks.
>
> Best regards,
> Yang

You are going to have to be more descriptive than this with setups and
problems.

As for real examples,  XenServer unconditionally sets up a native crash
kernel and does use it in the case of a Xen/dom0 crash.  It does work
reliably and repeatedly[1] and is routinely tested.

~Andrew

[1] We are aware of one hardware specific bug whereby the crash kernel
fails to set up a timer interrupt.  Investigating it is on my todo list.