On 08.05.14 03:33, Marcelo Tosatti wrote:
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 <ag...@suse.de>
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.
Well, the breakage occurs on the *source* of things. So if I have 100
VMs running, I'm pretty sure one of them gets hit by this bug.
If I put the workaround in the kernel, I have to take the chance to
break some of those 100 VMs to get things rolling. If I put it in QEMU,
I can live with a broken migration source.
This gets even worse when you want to phase out unfixed host kernels.
Alex
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