Revert "KVM: x86: use the fast way to invalidate all pages"

Revert to a slow kvm_mmu_zap_all() for kvm_arch_flush_shadow_all().
Flushing all shadow entries is only done during VM teardown, i.e.
kvm_arch_flush_shadow_all() is only called when the associated MM struct
is being released or when the VM instance is being freed.

Although the performance of teardown itself isn't critical, KVM should
still voluntarily schedule to play nice with the rest of the kernel;
but that can be done without the fast invalidate mechanism in a future
patch.

This reverts commit 6ca18b6950.

Cc: Xiao Guangrong <guangrong.xiao@gmail.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/mmu.c

@@ -5846,6 +5846,21 @@ void kvm_mmu_slot_set_dirty(struct kvm *kvm,
 }
 EXPORT_SYMBOL_GPL(kvm_mmu_slot_set_dirty);
 
+void kvm_mmu_zap_all(struct kvm *kvm)
+{
+	struct kvm_mmu_page *sp, *node;
+	LIST_HEAD(invalid_list);
+
+	spin_lock(&kvm->mmu_lock);
+restart:
+	list_for_each_entry_safe(sp, node, &kvm->arch.active_mmu_pages, link)
+		if (kvm_mmu_prepare_zap_page(kvm, sp, &invalid_list))
+			goto restart;
+
+	kvm_mmu_commit_zap_page(kvm, &invalid_list);
+	spin_unlock(&kvm->mmu_lock);
+}
+
 static void kvm_zap_obsolete_pages(struct kvm *kvm)
 {
 	struct kvm_mmu_page *sp, *node;

arch/x86/kvm/x86.c

@@ -9470,7 +9470,7 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
 
 void kvm_arch_flush_shadow_all(struct kvm *kvm)
 {
-	kvm_mmu_invalidate_zap_all_pages(kvm);
+	kvm_mmu_zap_all(kvm);
 }
 
 void kvm_arch_flush_shadow_memslot(struct kvm *kvm,