Re: [Qemu-devel] [PATCH] kvmclock: Ensure time in migration never goes backward

[Marcelo Tosatti]

On Mon, May 05, 2014 at 08:23:43PM -0300, Marcelo Tosatti wrote:
> Hi Alexander,
> 
> On Mon, May 05, 2014 at 03:51:22PM +0200, Alexander Graf wrote:
> > When we migrate we ask the kernel about its current belief on what the guest
> > time would be. 
> 
> KVM_GET_CLOCK which returns the time in "struct kvm_clock_data".
> 
> > However, I've seen cases where the kvmclock guest structure
> > indicates a time more recent than the kvm returned time.

This should not happen because the value returned by KVM_GET_CLOCK 
(get_kernel_ns() + kvmclock_offset) should be relatively in sync
with what is seen in the guest via kvmclock read.