Re: [Xen-devel] Fwd: Debugging "Xen BUG at ... list.h" on ARM

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Mon, 2014-04-14 at 10:30 +0100, Thomas Leonard wrote:
> On 14 April 2014 10:12, Julien Grall <julien.grall@xxxxxxxxxx> wrote:
> > (Adding a couple of people in cc)
> >
> > On 14/04/14 09:02, Thomas Leonard wrote:
> >>
> >> Hi all,
> >
> >
> > Hello,
> >
> >
> >> I'm new to Xen, and trying to get the arm32 port of Mini-OS working on
> >> a Cubieboard2. I have the board running an Ubuntu Dom0 and an Ubuntu
> >> guest happily, and I've written up the instructions for that here:
> >>
> >>
> >> https://github.com/talex5/mirage-www/blob/master/tmpl/wiki/xen-on-cubieboard2.md
> >>
> >> However, while trying to get a Mini-OS domU guest working I can now
> >> reliably crash the hypervisor. No doubt this is a bug in my guest
> >> code, but I assume it shouldn't be possible for a buggy guest to take
> >> down Xen itself.
> >>
> >> Here's a simplified version of my code which shows the problem:
> >>
> >>    https://github.com/talex5/xen-paratest
> >>
> >> I'm building Xen from the stable-4.4 Git branch (03eb51340), compiled
> >> with debug on.
> >>
> >> The code is rather simple: it's just trying to initialise the data
> >> cache, as described in the "ARM Cortex-A Series Programmerâs Guide".
> >> I'm not actually sure whether this is necessary for a paravirtualised
> >> guest, but I was getting some odd problems which looked cache related,
> >> so I added this code in the hope of fixing that.
> >
> >
> > Does it crash if you remove your cache code?
> 
> No, it just produces the wrong output in that case.
> 
> For background: I was making a hypervisor call to write out a string,
> then modifying a second string, then make a call to write that (both
> using HYPERVISOR_console_io).
> 
> Xen printed the second string with its first part containing the old
> text and the second part containing the new text. It looked like the
> old part was the bytes on the same cache line as the first string I
> printed, and I was trying to debug that.

Has your guest enabled caching (SCTLR.C)? This is required by the
hypercall ABI. See
http://xenbits.xen.org/docs/unstable/hypercall/arm/include,public,arch-arm.h.html#incontents_arm_abi

(the hypervisor still shouldn't crash though)

Ian.



_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel