Re: fedora 10 x86_64 breakage under KVM, due to KVM_CLOCK

[Avi Kivity <avi@redhat.com>]

Lennert Buytenhek wrote:
> (please CC, not on the list)
>
> Hi all,
>
> Fedora 10 randomly hangs for me when run under KVM, whereas (unpatched)
> F9 works fine.  When this happens, kvm_stat shows that the VM is seeing
> 1000 IRQ exits per second, but nothing else seems to happen.  The latest
> F9 update kernel seems to be bust as well.  (I noticed that the KVM guest
> support status page says that "Alexey E." is seeing the same thing.)
>
> I tried about two dozen different kernel packages from koji, and it turns
> out that kernel-2.6.26-0.122.rc9.git4.fc10 is the last known good kernel,
> and kernel-2.6.26-0.124.rc9.git5.fc10 is the first kernel that's broken.
>
> The F10 instability appears since this commit (attached below as well):
>
> 	http://fedora.gitbits.net/?p=kernel;a=commit;h=a5991f36968f44d4d3c64fc5aaa285a21de1ba54
>
> I built three new kernels from the latest 2.6.27-170.2.56.fc10 update
> in Fedora 10:
> 1. One with PARAVIRT and all associated options disabled entirely.
> 2. One with only KVM_GUEST disabled.
> 3. One with only KVM_CLOCK disabled (and paravirt and KVM_GUEST enabled).
>
> Kernel (1) is stable.  Kernel (2) is unstable like the unpatched F10
> kernels are, in that it randomly locks up.  Kernel (3) is stable as
> well, which suggests that KVM_CLOCK is what's causing the lockups.
>
> I tried booting the original F10 update kernel with no-kvmclock on
> the command line as well, and that makes things stable as well.
>
> I tried with the latest F10 updates-testing kernel (2.6.29.1-30.fc10),
> and that shows the same thing: with no-kvmclock it works fine, otherwise
> it hangs randomly.
>
> Running KVM 84 on x86_64 CentOS 5.3, with the kvm rpms from lfarkas.org.
> The host CPU is a Q6600 Core 2 Quad.
>
> Any ideas?
>   

This is a known issue.  While kvm-84 fixed kvmclock, an issue remained 
with cpu frequency scaling on older host kernels (including RHEL 5 / 
CentOS 5).  kvm-85 (to be released shortly) contains a fix (b395d156477a 
in kvm-userspace.git).


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