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Re: [Xen-devel] x86/AMD: Nested hvm crashes in 4.3

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@xxxxxxx> wrote:
On 6/27/2013 3:22 AM, Jan Beulich wrote:
On 27.06.13 at 02:24, Suravee Suthikulanit
<suravee.suthikulpanit@xxxxxxx> 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
which the issue started.

commit f1bde87fc08ce8c818a1640a8fe4765d48923091
Author: Jan Beulich <jbeulich@xxxxxxxx>
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@xxxxxxxx>
        Acked-by: Keir Fraser <keir@xxxxxxx>
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
"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


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
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,


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