Re: [Qemu-devel] Re: [PATCH] qemu-kvm: fix segfault when running kvm without /dev/kvm, falling back to non-accelerated mode

Luiz Capitulino
2009-09-04T21:39:34Z

On Fri, 4 Sep 2009 14:38:30 -0500
Dustin Kirkland <kirkland@canonical.com> wrote:

> On Fri, Sep 4, 2009 at 11:36 AM, Marcelo Tosatti<mtosatti@redhat.com> wrote:
> > On Fri, Sep 04, 2009 at 11:06:38AM -0500, Dustin Kirkland wrote:
> >> On Fri, 2009-09-04 at 08:22 +0100, Mark McLoughlin wrote:
> >> > On Thu, 2009-09-03 at 19:18 -0300, Glauber Costa wrote:
> >> > > On Thu, Sep 3, 2009 at 6:48 PM, Dustin Kirkland<kirkland@canonical.com> wrote:
> >> > > > On Thu, Sep 3, 2009 at 3:01 PM, Mark McLoughlin<markmc@redhat.com> wrote:
> >> > > >> On Thu, 2009-09-03 at 12:31 -0500, Dustin Kirkland wrote:
> >> > > >>> qemu-kvm: fix segfault when running kvm without /dev/kvm, falling back
> >> > > >>> to non-accelerated mode
> >> > > >>>
> >> > > >>> We're seeing segfaults on systems without access to /dev/kvm.  It
> >> > > >>> looks like the global kvm_allowed is being set just a little too late
> >> > > >>> in vl.c.  This patch moves the kvm initialization a bit higher in the
> >> > > >>> vl.c main, just after options processing, and solves the segfaults.
> >> > > >>> We're carrying this patch in Ubuntu 9.10 Alpha.  Please apply
> >> > > >>> upstream, or advise if and why this might not be the optimal solution.
> >> > > >>
> >> > > >> Ah discussion about an alternative fix for this fizzled out recently:
> >> > > >>
> >> > > >>  http://www.mail-archive.com/kvm@vger.kernel.org/msg19890.html
> >> > > >
> >> > > > Ah, thanks Mark.  In that thread, I found Daniel's suggestion the most
> >> > > > reasonable, and user-friendly:
> >> > > >
> >> > > > On Mon, Jul 27, 2009 at 1:44 PM, Daniel P. Berrange<berrange@redhat.com> wrote:
> >> > > >> Well, we could go for logic like:
> >> > > >>
> >> > > >>  * No arg given          => try kvm, try kqemu, try tcg
> >> > > >>  * --accelmode arg given => try $arg, and fail if unavailable
> >> > > >>
> >> > > >> then libvirt would simply always supply --accelmode for all VMs,
> >> > > >> while people running qemu manually would get best available
> >> > > I sent some patches to do that, but they were incomplete, and I was
> >> > > preempted by something else.
> >> > > If you want, you can wait for my cycles to come back, or pick from where I left
> >>
> >> Thanks for the pointer, Glauber.  My cycles a bit constrained too, but
> >> I'll have a look when I get a chance.
> >>
> >> > In the meantime, can we commit to stable-0.11 either Dustin's fix or
> >> > this:
> >> >
> >> >   http://git.et.redhat.com/?p=qemu-fedora.git;a=commitdiff;h=aa1620047b
> >>
> >> +1.  We're looking for something agreeable in stable-0.11, that solves
> >> the segfault and proceeds without VT acceleration.
> >
> > Dustin,
> >
> > Can you please resend the patch with the suggestion i made earlier, for
> > stable-0.11?
>
> Sure, Marcelo. It's attached.
>
> I tested it, and it still does avoid the segfault.
>
> Luiz, could you re-test this patch on your side too?

I'm getting rejections, are you sure it's against upstream?