On Mon, 6/8/09, Avi Kivity wrote:
> Adam Richter wrote:
> > Hi everyone,
> >
> > I have a qcow2 image that runs fine under kubuntu 8.04
> with kvm for kernels up to 2.6.29. However, for
> 2.6.29-git1 and every kernel that I have tried thereafter
> including 2.6.30-rc8-git1, I get a kernel oops when I try to
> run kvm on this image.
> >
> > From the stack traces that I see, it is possible that
> the bug is not in kvm, but rather in some filesystem
> code. However, fs/ext3/inode.c was the only file in
> fs/ext3 updated between 2.6.29 and 2.6.29-git1, and the
> problem persisisted after I reverted that change in
> 2.6.29-git1.
> >
> > I should also add that, on another Linux computer,
> which is not running Kubuntu, I got a kernel oops when
> trying to rsync an image I use with kvm when I was also
> using a post-2.6.29 kernel. It is possible that I had
> run kvm on that file since booting the computer and before
> doing the rsync, but I am not sure. So, it is possible
> that there might be bug where kvm somehow breaks dentry or
> inode information, which results in an oops later in the
> file system code, or it may still be possible that the bug
> is purely a file system bug.
> >
> > I have done a few iterations of git bisect, but I do
> not think I will have time to do the ~10 more that will be
> necessary for it to converge (assuming no versions in the
> middle with serious compilation problems). So, I am
> posting this information now.
> >
> > The rest of this message is just information to help
> anyone who thinks they recognize this bug to determine if
> this is likely the same bug. I'll post a follow-up if
> and when I complete the git bisect, assuming that I do not
> learn that this problem has already been solved. If
> anyone recognizes this problem as having a known fix, please
> let me know so that I can stop duplicating your efforts.
> >
> >
>
> This is a guest kernel oops, right?
No. The host kernel gets the oops, causing the the "kvm" program to exit with a fake kill signal from the kernel. I believe that the oops occurs before the grub bootloader on the guest has started running, much less booted any operating system.
> When you change the kernel, do you mean the host kernel or
> guest kernel?
Host kernel.
> What arch and pae-ness are the guest and host running?
The guest kernel that the target OS uses happens to be non-PAE, but I do not believe that the guest kernel is even copied into memory on the guest virtual machine before the kernel oops on the host computer.
I have reproduced the problem with both PAE and non-PAE host configurations of the same linux-2.6.30-rc8-git5 source tree.
By the way, I apparently twice botched the git bisect search I was doing on this problem, and am in the process of trying for a third time. I will let you know if and when I have a result from that.
Thank you for considering this problem.
Adam Richter
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