KVM: x86: update masterclock when kvmclock_offset is calculated

[Marcelo Tosatti <mtosatti@redhat.com>]

The offset to add to the hosts monotonic time, kvmclock_offset, is
calculated against the monotonic time at KVM_SET_CLOCK ioctl time.

Request a master clock update at this time, to reduce a potentially
unbounded difference between the values of the masterclock and
the clock value used to calculate kvmclock_offset.

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

Index: linux-2.6-kvmclock-fixes/arch/x86/kvm/x86.c
===================================================================
--- linux-2.6-kvmclock-fixes.orig/arch/x86/kvm/x86.c
+++ linux-2.6-kvmclock-fixes/arch/x86/kvm/x86.c
@@ -3806,6 +3806,7 @@ long kvm_arch_vm_ioctl(struct file *filp
 		delta = user_ns.clock - now_ns;
 		local_irq_enable();
 		kvm->arch.kvmclock_offset = delta;
+		kvm_gen_update_masterclock(kvm);
 		break;
 	}
 	case KVM_GET_CLOCK: {