[PROBLEM] Guest with SMP >=2 with kvm_clock has jumping clock every few seconds

[John Buswell <buswellj@carbonmountain.com>]

I ran into the problem below running 2.6.33.2:

Problem: KVM guest running Linux 2.6.33.2 with kvm_clock as the clock 
source and more than 1 virtual CPU has the clock jumping forward 1 hour, 
13 minutes and 17 seconds (consistently)

Hardware: AMD Athlon Dual Core 4850e @ 2511.769 MHz

I can reproduce this consistently, and it does not happen on the same 
machine if I launch the same KVM guest with -smp 1.

With RTC compiled into the kernel you can see that its just clock, the 
localtime was set to UTC:

Running the following in a loop:

cat /sys/class/rtc/rtc0/time ; date

You see:

18:07:49
Mon Apr 12 18:07:49 UTC 2010

18:08:21
Mon Apr 12 19:21:49 UTC 2010

18:08:21
Mon Apr 12 18:08:22 UTC 2010

The load average on the system is 0, the guest is doing nothing but 
running init. It happens regardless of whether I run one guest or over 
10 guests on the same system.

I can easily reproduce this issue, so if you need someone to test 
patches etc, I can easily do that.

Thanks

-- 
John Buswell
http://www.carbonmountain.com