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Re: [Xen-devel] General protection fault in netback

On Tue, Feb 21, 2012 at 06:06:14PM +0300, Anton Samsonov wrote:
> 2012/2/15 Pasi Kärkkäinen <pasik@xxxxxx>:
> AS>> Unfortunately, I'm not skilled at compiling the kernel myself.
> AS>> I tried building the newest 3.2.6 with all Xen options enabled,
> AS>> but the resulting system didn't have netback.ko module at all,
> AS>> barely booted, and xm was not able to communicate with VMM.
> PK> About compiling the dom0 kernel, see this wiki page:
> PK> http://wiki.xen.org/wiki/XenParavirtOps#Configure_kernel_for_dom0_support
> Thanks, it looks like I just messed some "y" with "m" and vice versa
> ("m" is presented as a meaningless bullet in GUI). By the way, that how-to
> contains dubious lines for CONFIG_XEN_DEV_EVTCHN and CONFIG_XEN_GNTDEV.
> Well, now the system boots more eagerly, although the kernel still
> seems to be slightly incompatible with distro's environment and my hardware.
> But at least xend is now responding and is able to run DomUs as usual.
> I started and stopped all the swarm of VMs several times (without letting them
> to run for some time), and observed no GPF. But instead of this I get
> screen garbling: while a DomU is starting or stopping, the whole graphical
> desktop is sometimes painted with either black or not-so-random garbage,
> and even mouse pointer can become garbled; I have to move / resize windows
> to get them repainted. Network connectivity between Dom0 and [subsequently
> started] DomUs does not break though.
> On one hand, I am not sure whether the video driver is not to be
> blamed for glitches,
> because graphics already does not work as usual: it is not 
> hardware-accelerated
> with my custom kernel (while it is with stock kernel), and the screen is 
> garbled
> on Xorg startup, before login promt is displayed. On the other hand, this is 
> not

So... I am curious, what graphic card do you have and do you get any of
these Red Hat BZs?  RH BZ# 742032, 787403, and 745574?

> in any way normal, as Xen operations must not interfere with Dom0's desktop
> (or was it direct VRAM corruption?).

It is complicated. There is a bug in 3.2 when using radeon or nouveau for a 
time of period that ends up "corrupting" memory. The workaround is to provide 
on the argument line.

> This happens even when "suspicious" domains (NetBSD with CARP) are not
> started: on a freshly booted Dom0, just having 4 essential DomUs is enough
> to get that screen garbling when shutting down 1 or 2 of them for the
> first time.

Hmm, that is weird. Never seen that before. Can you include more details on your

> But when I return to stock kernel, I can run a dozen of such DomUs (including
> those NetBSD load-balancers), starting and stopping them many times
> without a problem. Recently, no GPF occurred when only 1 out of 2 balancers
> is started, or none of them started at all; or it just needs much more uptime
> to accumulate memory corruption for a GPF.
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