Re: x86/AMD: Nested hvm crashes in 4.3

[Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>]

On 6/27/2013 3:22 AM, Jan Beulich wrote:
>>>> On 27.06.13 at 02:24, Suravee Suthikulanit <suravee.suthikulpanit@amd.com> wrote:
>> I have found an issue in where the system crash right when I start
>> another HVM guest inside an HVM guest.  I have traced back to the patch
>> which the issue started.
>>
>> commit f1bde87fc08ce8c818a1640a8fe4765d48923091
>> Author: Jan Beulich <jbeulich@suse.com>
>> Date:   Fri Feb 8 11:06:04 2013 +0100
>>
>>       x86: debugging code for testing 16Tb support on smaller memory systems
>>
>>       Signed-off-by: Jan Beulich <jbeulich@suse.com>
>>       Acked-by: Keir Fraser <keir@xen.org>
> We had issues exposed by this patch before, but any such issue
> would just have been masked before that patch (and would
> surface on a system with more than 5Tb of memory anyway).

The system I am having the issue has 48GB of memory.

> So it is very unlikely for the patch itself to be at fault.

I have traced the issue and found that the system crashing starts from this commit id and onward.
(i.e. The system does not crash with commit id ed759d20249197cf87b338ff0ed328052ca3b8e7)
So, I am still believe that this patch has somehow triggered the issue.

> Furthermore, the crash them supposedly is because of the code
> added conditional upon NDEBUG, and hence would (on a smaller
> memory system) otherwise not surface at all for a production
> (debug=n) build.
>
>> The issue doesn't reproduce when starting a PV (L2) guest inside an HVM
>> (L1) guest.
> "Does not" or "does"? In the former case - what is this supposed to
> tell me?

What I am trying to say here is that the system_does not_ crash when starting the PV guest as level 2 guest.
This is meant to be another data point to help analyzing the issue.

> In any case - without you sharing technical details (register/stack
> dump of the crash at the very least) I don't think I have anything
> at hand to look for possible problems.

At this point, I am just reporting the issue.  I have not been able to get the crash dump because the system immediately reboot.
I'll try to boot Xen with "noreboot" and inspect the log for more clues. Any suggestions are welcome.

Thank you,

Suravee

>
> Jan
>
>