KVM: x86: Avoid zapping mmio sptes twice for generation wraparound

Now that kvm_arch_memslots_updated() catches every increment of the
memslots->generation, checking if the mmio generation has reached its
maximum value is enough.
Signed-off-by: NTakuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp>
Reviewed-by: NXiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/mmu.c

@@ -4390,11 +4390,8 @@ void kvm_mmu_invalidate_mmio_sptes(struct kvm *kvm)
 	/*
 	 * The very rare case: if the generation-number is round,
 	 * zap all shadow pages.
-	 *
-	 * The max value is MMIO_MAX_GEN - 1 since it is not called
-	 * when mark memslot invalid.
 	 */
-	if (unlikely(kvm_current_mmio_generation(kvm) >= (MMIO_MAX_GEN - 1))) {
+	if (unlikely(kvm_current_mmio_generation(kvm) >= MMIO_MAX_GEN)) {
 		printk_ratelimited(KERN_INFO "kvm: zapping shadow pages for mmio generation wraparound\n");
 		kvm_mmu_invalidate_zap_all_pages(kvm);
 	}

arch/x86/kvm/x86.c

@@ -7021,6 +7021,11 @@ int kvm_arch_create_memslot(struct kvm_memory_slot *slot, unsigned long npages)
 
 void kvm_arch_memslots_updated(struct kvm *kvm)
 {
+	/*
+	 * memslots->generation has been incremented.
+	 * mmio generation may have reached its maximum value.
+	 */
+	kvm_mmu_invalidate_mmio_sptes(kvm);
 }
 
 int kvm_arch_prepare_memory_region(struct kvm *kvm,
@@ -7083,11 +7088,6 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
 	 */
 	if ((change != KVM_MR_DELETE) && (mem->flags & KVM_MEM_LOG_DIRTY_PAGES))
 		kvm_mmu_slot_remove_write_access(kvm, mem->slot);
-	/*
-	 * If memory slot is created, or moved, we need to clear all
-	 * mmio sptes.
-	 */
-	kvm_mmu_invalidate_mmio_sptes(kvm);
 }
 
 void kvm_arch_flush_shadow_all(struct kvm *kvm)