Re: BUG: unable to handle kernel paging request - balloon_init - xen-4.1.0 - 2.6.32.39

[Scott Garron <xen-devel@sce.pridelands.org>]

On 4/29/2011 10:43 AM, Dan Magenheimer wrote:
> That multiply is correct.  In C, when you add an integer X to a
> pointer to a struct of size N, the result is the same as if you were
>  accessing the Xth element of an array of those structs.

      Oh yeah!  I completely forgot about that.  (Haven't done any
programming for about six years, so ... rusty)

> 1) Is your guest an HVM or PV?  IIRC, earlier versions of the
> balloon driver did not run properly in an HVM guest.  Compare your
> source with a latest upstream balloon_init.

      This machine is too old to have the ability to run a guest as HVM
(it's pre-Pacifica/AMD-V), but the problem isn't with running a domU.
It won't boot into dom0 (privileged domain) due to this bug.  Oddly
enough, the build in question *does* work as a PV domU when the hardware
is booted to the Debian stock linux-image-xen-amd64 kernel
(2.6.32-5-xen-amd64).

> 2) Are you building xen/stable-2.6.32.x as the kernel in a guest?
> Any chance you might be loading a balloon module that doesn't match
> the kernel you built?

      I'm building the kernel on a separate, faster machine than the one
I'm trying to boot it on.  I wasn't aware that where it was being built
made much of a difference as long as the configured processor type was
correct.  Both machines are x86_64, but one is Xeon and the other is
Opteron.  If it does matter where it's built, how do distributions put
out pre-compiled dom0 kernels?  Also, if it does matter, I can try
building it on the slower machine.  (The faster one is a production
server, so I'm not testing all of these reboots on that)

> 3) I think developers generally use the xen/stable-2.6.32.x for dom0
> and use distro kernels (or newer upstream kernels) for guest kernels.
> So it is very possible that you are the only one having this problem
> because you are the only one using a balloon driver on a
> xen/stable-2.6.32.x kernel in a non-dom0 (HVM?) guest.

      I *am* trying to use it in a dom0 guest.  It's:

Hardware/BIOS -> Xen4.1 -> this xen/stable-2.6.32.x dom0 -> crash

> 4) The latest upstream balloon driver does some magic with the E820
> memory map.  Perhaps your machine has an odd or incorrect E820 map
> from the BIOS?  (This is outside of my area of expertise so apologies
> if this doesn't make sense.)

      I suppose it could be odd.  The machine is about 8 years old.  I'd
imagine that they were doing things a bit differently back then.

-- 
Scott Garron