KVM: MMU: do not reuse the obsolete page

The obsolete page will be zapped soon, do not reuse it to
reduce future page fault

Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Reviewed-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 3fd060a..0880b9b4 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -1875,6 +1875,9 @@
 		role.quadrant = quadrant;
 	}
 	for_each_gfn_sp(vcpu->kvm, sp, gfn) {
+		if (is_obsolete_sp(vcpu->kvm, sp))
+			continue;
+
 		if (!need_sync && sp->unsync)
 			need_sync = true;