Re: [BUG] kvm crashes in 2.6.28-rc6-00007-ged31348

From: Luis Henriques
Date: Tue Dec 02 2008 - 14:46:32 EST

(I am CC'ing to Steven Rostedt since he might be interested on this)

On Tue, Dec 02, 2008 at 07:09:14PM +0000, Luis Henriques wrote:
> On Tue, Dec 02, 2008 at 02:23:52PM +0200, Avi Kivity wrote:
> > Luis Henriques wrote:
> >> On Sun, Nov 30, 2008 at 10:44:55PM +0200, Avi Kivity wrote:
> >>
> >>> Luis Henriques wrote:
> >>>
> >>>> No, I was not able to reproduce the issue. Please let me know if you need some
> >>>> more information on my system (.config, for instance).
> >>>>
> >>> Were you using some other virtualization product? Were you running
> >>> suspend/resume?
> >>>
> >>
> >> No for both questions. However, I had compiled support for suspend (not sure if
> >> this is what you mean by "running suspend/resume") - This is a feature I used
> >> only once or twice...
> >>
> >
> > The underlying problem is that an svm instruction has been executed, but
> > svm is disabled. Since kvm enables svm unconditionally on all
> > processors on startup, there are only a few paths that can potentially
> > trigger this:
> >
> > - another virtualization module turned svm off
> > - cpu hotadd/hotremove (suspend/resume triggers this)
> > - something did a read-modify-write cycle on cr4 (which contains the svm
> > enable bit) while kvm enabled that bit
> > - core was turned off (does linux power management do that?)
> >
> > Anything ring a bell?
> Ok, I am not sure but there is a possibility of having the vboxdrv driver
> loaded. _But_ I was not using, i.e., I do not use VirtualBox. In my
> attempts to reproduce the issue, I tried to load this module but, unfortunatly,
> my distro has this package broken ATM (err... in fact, the problem is not the
> distro but me - I am using an unstable version).
> vboxdrv could be a problem if I was using it, but I believe it shouldn't cause
> this if it is not being used... but it's just a guess.

I have some other information to had to my previous email. However, I do not
know whether it is related with my first bug report.

It looks like ftrace may stop the CPUs in some situations and I have been
playing with ftrace for some time. So, here's what I just did: started ftrace
with function tracer and then started kvm. I got ugly crashes and apparently
quite easy to reproduce (I get complete freeze or immediate reboot).

I did not investigated this issue and, again, it may not be related with my
initial report but there's definitely something wrong here, right?

(just to refresh, I am using 2.6.28-rc6-00007-ged31348 in x86_64 machine)

Luis Henriques

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