When we use dependent clock in domU, the time syncing from Dom0 to DomU is monotonic (in xenified kernel 188.8.131.52 ).
While, when I read the source code of arch/i386/time-xen.c, I think we can allow the backward time syncing by reset the monotonic time value (monotonic.tv) when the HYPERVISOR_shared_info->wc_version is changed.
I’ve tested that, whenever the Dom0 time changed, the domU’s time would be sync-ed immediately. (with /proc/sys/xen/independent_wallclock=0 ).
So, seems it works perfect, it’s a real dependent wall clock now.
It’s easy to implement the backward time syncing.
So, I wonder that, are there some risks to allow the backward time syncing?
If there isn’t known risk, I’d like to send a patch to allow the backward time syncing.
Could you anybody can help to understand the risks?
Any input is appreciated.