KVM: MMU: support disable/enable mmu audit dynamicly

Add a r/w module parameter named 'mmu_audit', it can control audit
enable/disable:

enable:
  echo 1 > /sys/module/kvm/parameters/mmu_audit

disable:
  echo 0 > /sys/module/kvm/parameters/mmu_audit

This patch not change the logic

Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index a0f2feb..debe770 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -542,7 +542,7 @@
 	if (mmu_notifier_retry(vcpu, mmu_seq))
 		goto out_unlock;
 
-	kvm_mmu_audit(vcpu, "pre page fault");
+	trace_kvm_mmu_audit(vcpu, AUDIT_PRE_PAGE_FAULT);
 	kvm_mmu_free_some_pages(vcpu);
 	sptep = FNAME(fetch)(vcpu, addr, &walker, user_fault, write_fault,
 			     level, &write_pt, pfn);
@@ -554,7 +554,7 @@
 		vcpu->arch.last_pt_write_count = 0; /* reset fork detector */
 
 	++vcpu->stat.pf_fixed;
-	kvm_mmu_audit(vcpu, "post page fault (fixed)");
+	trace_kvm_mmu_audit(vcpu, AUDIT_POST_PAGE_FAULT);
 	spin_unlock(&vcpu->kvm->mmu_lock);
 
 	return write_pt;