port-xen/47056: Xen NetBSD DomU freeze under Linux Dom0

[royger%netbsd.org@localhost]

>Number:         47056
>Category:       port-xen
>Synopsis:       Xen NetBSD DomU freeze under Linux Dom0
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    port-xen-maintainer
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Oct 11 17:05:00 +0000 2012
>Originator:     Roger Pau Monné
>Release:        6.0RC2
>Organization:
Citrix
>Environment:
NetBSD  6.0_RC2 NetBSD 6.0_RC2 (XEN3_DOMU) #6: Wed Sep 26 18:06:29 BST 2012  
root@roger-xen:/root/obj/sys/arch/amd64/compile/XEN3_DOMU amd64
>Description:
The simptoms are that
the DomU is frozen and xentop on Dom0 shows CPU usage of 100% (so it's a
busy-wait). I went further on this, and the culprit of the freeze was
this line in sys/arch/xen/xenbus/xenbus_xs.c:

831 printk("XENBUS error %d while reading message\n", err);

Going further, replacing this line with a regular panic made the kernel
panic (obvious), and the root cause of this panic is the fact that the
ring indexes in xenstore_interface global variable get completely
corrupted, they jump from ~400 to ~30000, which shows that we have a
memory corruption problem in my opinion.
>How-To-Repeat:
I've been able to reproduce this using a Debian Dom0 (with Linux kernel
2.6.32 and 3.2) with 4vcpus. The procedure is to create a NetBSD DomU,
and try to perform a NetBSD build from sources. I haven't been able to
finish any build inside of a DomU using a Linux Dom0.
>Fix: