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Re: [Xen-devel] [PATCHv10 0/9] Xen: extend kexec hypercall for use with pv-ops kernels

On 07/11/13 21:16, Daniel Kiper wrote:
> On Wed, Nov 06, 2013 at 02:49:37PM +0000, David Vrabel wrote:
>> The series (for Xen 4.4) improves the kexec hypercall by making Xen
>> responsible for loading and relocating the image.  This allows kexec
>> to be usable by pv-ops kernels and should allow kexec to be usable
>> from a HVM or PVH privileged domain.
>> I have now tested this with a Linux kernel image using the VGA console
>> which was what was causing problems in v9 (this turned out to be a
>> kexec-tools bug).
>> The required patch series for kexec-tools will be posted shortly and
>> are available from the xen-v7 branch of:
> In general it works. However, quite often I am not able to execute panic
> kernel. Machine hangs with following message:
> (XEN) Domain 0 crashed: Executing crash image
> gdb shows:
> (gdb) bt
> #0  0xffff82d0801a0092 in do_nmi_crash (regs=<optimized out>) at crash.c:113
> #1  0xffff82d0802281d9 in nmi_crash () at entry.S:666
> #2  0x0000000000000000 in ?? ()
> (gdb)
> Especially second bt line scares me... ;-)))

Why? This is completely normal.  If you look in crash.c at that line, it
is a for (;;) halt(); loop

How are you hooking gdb up?

> I have not been able to identify why NMI was activated because
> stack is completely cleared. I tried to record execution in gdb
> but it stops with following message:

NMIs are used for cpu shootdown of the non-crashing cpus.  Again, this
is not touched by the series.


> cpumask_clear_cpu (dstp=0xffff82d0802f7f78 <call_data+24>, cpu=0)
>     at /srv/dev/xen/xen_20130413_20131107.kexec/xen/include/xen/cpumask.h:108
> 108             clear_bit(cpumask_check(cpu), dstp->bits);
> Process record: failed to record execution log.
> Do you know how to find out why NMI was activated?
> I am able almost always reproduce this issue doing this:
>   - boot Xen,
>   - load panic kernel,
>   - echo c > /proc/sysrq-trigger,
>   - reboot from command line,
>   - boot Xen,
>   - load panic kernel,
>   - echo c > /proc/sysrq-trigger.
> Additionally, my compiler fails because it detects unused result
> variable in xen/common/kimage.c:kimage_crash_alloc().
> Daniel
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