KVM: x86: workaround SuSE's 2.6.16 pvclock vs masterclock issue

KVM: x86: workaround SuSE's 2.6.16 pvclock vs masterclock issue

SuSE's 2.6.16 kernel fails to boot if the delta between tsc_timestamp
and rdtsc is larger than a given threshold:

 * If we get more than the below threshold into the future, we rerequest
 * the real time from the host again which has only little offset then
 * that we need to adjust using the TSC.
 *
 * For now that threshold is 1/5th of a jiffie. That should be good
 * enough accuracy for completely broken systems, but also give us swing
 * to not call out to the host all the time.
 */
#define PVCLOCK_DELTA_MAX ((1000000000ULL / HZ) / 5)

Disable masterclock support (which increases said delta) in case the
boot vcpu does not use MSR_KVM_SYSTEM_TIME_NEW.

Upstreams kernels which support pvclock vsyscalls (and therefore make
use of PVCLOCK_STABLE_BIT) use MSR_KVM_SYSTEM_TIME_NEW.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>