kvmclock currently falls apart on machines without constant tsc.
This patch fixes it. Changes:
* keep tsc frequency in a per-cpu variable.
* handle kvmclock update using a new request flag, thus checking
whenever we need an update each time we enter guest context.
* use a cpufreq notifier to track frequency changes and force
kvmclock updates.
* send ipis to kick cpu out of guest context if needed to make
sure the guest doesn't see stale values.
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
c807660407