KVM: MMU: don't get free page number in the loop

In the later patch, we will modify sp's zapping way like below:

	kvm_mmu_prepare_zap_page A
	kvm_mmu_prepare_zap_page B
	kvm_mmu_prepare_zap_page C
	....
	kvm_mmu_commit_zap_page

[ zaped multiple sps only need to call kvm_mmu_commit_zap_page once ]

In __kvm_mmu_free_some_pages() function, the free page number is
getted form 'vcpu->kvm->arch.n_free_mmu_pages' in loop, it will
hinders us to apply kvm_mmu_prepare_zap_page() and kvm_mmu_commit_zap_page()
since kvm_mmu_prepare_zap_page() not free sp.
Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

arch/x86/kvm/mmu.c

@@ -2863,13 +2863,16 @@ EXPORT_SYMBOL_GPL(kvm_mmu_unprotect_page_virt);
 
 void __kvm_mmu_free_some_pages(struct kvm_vcpu *vcpu)
 {
-	while (vcpu->kvm->arch.n_free_mmu_pages < KVM_REFILL_PAGES &&
+	int free_pages;
+
+	free_pages = vcpu->kvm->arch.n_free_mmu_pages;
+	while (free_pages < KVM_REFILL_PAGES &&
 	       !list_empty(&vcpu->kvm->arch.active_mmu_pages)) {
 		struct kvm_mmu_page *sp;
 
 		sp = container_of(vcpu->kvm->arch.active_mmu_pages.prev,
 				  struct kvm_mmu_page, link);
-		kvm_mmu_zap_page(vcpu->kvm, sp);
+		free_pages += kvm_mmu_zap_page(vcpu->kvm, sp);
 		++vcpu->kvm->stat.mmu_recycled;
 	}
 }