RHEL5.5, 32-bit VM repeatedly locks up due to kvmclock

["David S. Ahern" <daahern@cisco.com>]

After a few days of debugging I think kvmclock is the source of lockups
for a RHEL5.5-based VM. The VM works fine on one host, but repeatedly
locks up on another.

Server 1 - VM locks up repeatedly
-- DL580 G5
-- 4 quad-core X7350 processors at 2.93GHz
-- 48GB RAM

Server 2 - VM works just fine
-- DL380 G6
-- 2 quad-core E5540 processors at 2.53GHz
-- 24GB RAM

Both host servers are running Fedora Core 12, 2.6.32.11-99.fc12.x86_64
kernel. I have tried various versions of qemu-kvm -- the version in
FC-12 and the version for FC-12 in virt-preview. In both cases the
qemu-kvm command line is identical.

VM
- RHEL5.5, PAE kernel (also tried standard 32-bit)
- 2 vcpus
- 3GB RAM
- virtio network and disk

When the VM locks up both vcpu threads are spinning at 100%. Changing
the clocksource to jiffies appears to have addressed the problem.

David