KVM: MMU: delay local tlb flush

delay local tlb flush until enter guest moden, it can reduce vpid flush
frequency and reduce remote tlb flush IPI(if KVM_REQ_TLB_FLUSH bit is
already set, IPI is not sent)
Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

arch/x86/kvm/mmu.c

@@ -2364,7 +2364,7 @@ static int nonpaging_init_context(struct kvm_vcpu *vcpu)
 void kvm_mmu_flush_tlb(struct kvm_vcpu *vcpu)
 {
 	++vcpu->stat.tlb_flush;
-	kvm_x86_ops->tlb_flush(vcpu);
+	set_bit(KVM_REQ_TLB_FLUSH, &vcpu->requests);
 }
 
 static void paging_new_cr3(struct kvm_vcpu *vcpu)