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

[Marcelo Tosatti]

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. However, I've seen cases where the kvmclock guest structure
> indicates a time more recent than the kvm returned time.
> 
> To make sure we never go backwards, calculate what the guest would have seen
> as time at the point of migration and use that value instead of the kernel
> returned one when it's more recent.
> 
> While this doesn't fix the underlying issue that the kernel's view of time
> is skewed, it allows us to safely migrate guests even from sources that are
> known broken.
> 
> Signed-off-by: Alexander Graf <address@hidden>

OK Alexander better move this logic to the kernel, in KVM_GET_CLOCK.

Otherwise every user of KVM_GET_CLOCK would have to apply the
workaround.