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

[Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>]

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
> > > > > > patch
> > > > > > 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
> > 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




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