Re: x86/AMD: Nested hvm crashes in 4.3

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

On 6/27/2013 5:33 AM, Egger, Christoph wrote:
> On 27.06.13 12:24, Suravee Suthikulpanit wrote:
>> On 6/27/2013 5:08 AM, Jan Beulich wrote:
>>>>>> On 27.06.13 at 11:20, Suravee Suthikulpanit
>>>>>> <suravee.suthikulpanit@amd.com> wrote:
>>>> 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.
>>> Which is why you're seeing the problem only with the debugging
>>> code enabled.
>> Is the "debugging" enabled by default?  I didn't specify any debug when
>> building.
> "Debugging" is enabled by default in the development tree.
>
>> How can I check and disable debugging?
> In the toplevel source directory look into Config.mk
> and set the line
>
>     debug ?= y
>
> accordingly.

Thank you for clarification.

>>> (And of course I didn't really expect you to have
>>> tried this on a huge memory system - they're just too rare still
>>> for this to be likely.)
>>>
>>>>> 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.
>>> As said - I'm pretty certain this merely unmasked an already
>>> lurking issue.
>> I'm not quite sure what you meant here.  Are you saying that this
>> "crashing" is a known issue?
> He means nestedhvm reveals an existing bug in his patch.
> If he is right then you do not see nestedhvm crashing with a non-debug
> xen-kernel (unless something else broke it).

After I rebuilt Xen kernel with debug=n, the system no longer crash when starting npt-on-npt and shadown-on-npt guests.
I was not able to get to the crash dump previously. I will try again tomorrow at work and will post them.

Thank you,

Suravee