KVM: Don't bother the mmu if cr3 load doesn't change cr3

If the guest requests just a tlb flush, don't take the vm lock and
drop the mmu context pointlessly.

Signed-off-by: Avi Kivity <avi@qumranet.com>
diff --git a/drivers/kvm/mmu.c b/drivers/kvm/mmu.c
index 281dd5f..346aa65 100644
--- a/drivers/kvm/mmu.c
+++ b/drivers/kvm/mmu.c
@@ -1086,7 +1086,7 @@
 	return 0;
 }
 
-static void kvm_mmu_flush_tlb(struct kvm_vcpu *vcpu)
+void kvm_mmu_flush_tlb(struct kvm_vcpu *vcpu)
 {
 	++vcpu->stat.tlb_flush;
 	kvm_x86_ops->tlb_flush(vcpu);