how to keep time of windows pvhvm synchronized with host after resuming

[ANNIE LI <annie.li@oracle.com>]

Hi

When the virtual machine is resumed from suspend, the guest operating 
system's wall-clock time remains at the value it had at the time of the 
suspension. For linux pvm, we can avoid resolve issue by setting 
independent_wallclock=0. However, HVM(or PVHVM) does not support this 
feature.

I did some investigation on how to implement this in windows 
para-virtualization driver. In \include\xen\interface\xen.h, there are 
several variables about timer such as: wc_sec and wc_nsec, and 
vcpu_time_info struct. It is very strange, wc_sec and wc_nsec is always 
zero for my windows vm with para-virtualization driver. Vcpu_time_info 
only contains time info for specific vcpu. Should i use those variables 
to get accurate time for VM? Is there any corresponding source code or 
algorithms available now? Is it safe to simply update vm time after 
resuming?

Citrix 5.6 Windows para-virtualization driver will notify windows kernel 
time change after resuming, and resumed windows vm with Citrix pv driver 
can keep it's time synchronized with host. Would you like to give me 
some clues about how to implement this?

Any help is greatly appreciated.

Thanks
Annie