KVM: x86/mmu: Factor out functions to add/remove TDP MMU pages

Move the work of adding and removing TDP MMU pages to/from  "secondary"
data structures to helper functions. These functions will be built on in
future commits to enable MMU operations to proceed (mostly) in parallel.

No functional change expected.
Signed-off-by: Ben Gardon <bgardon@google.com>
Message-Id: <20210202185734.1680553-20-bgardon@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/mmu/tdp_mmu.c

@@ -262,6 +262,39 @@ static void handle_changed_spte_dirty_log(struct kvm *kvm, int as_id, gfn_t gfn,
 	}
 }
 
+/**
+ * tdp_mmu_link_page - Add a new page to the list of pages used by the TDP MMU
+ *
+ * @kvm: kvm instance
+ * @sp: the new page
+ * @account_nx: This page replaces a NX large page and should be marked for
+ *		eventual reclaim.
+ */
+static void tdp_mmu_link_page(struct kvm *kvm, struct kvm_mmu_page *sp,
+			      bool account_nx)
+{
+	lockdep_assert_held_write(&kvm->mmu_lock);
+
+	list_add(&sp->link, &kvm->arch.tdp_mmu_pages);
+	if (account_nx)
+		account_huge_nx_page(kvm, sp);
+}
+
+/**
+ * tdp_mmu_unlink_page - Remove page from the list of pages used by the TDP MMU
+ *
+ * @kvm: kvm instance
+ * @sp: the page to be removed
+ */
+static void tdp_mmu_unlink_page(struct kvm *kvm, struct kvm_mmu_page *sp)
+{
+	lockdep_assert_held_write(&kvm->mmu_lock);
+
+	list_del(&sp->link);
+	if (sp->lpage_disallowed)
+		unaccount_huge_nx_page(kvm, sp);
+}
+
 /**
  * handle_removed_tdp_mmu_page - handle a pt removed from the TDP structure
  *
@@ -281,10 +314,7 @@ static void handle_removed_tdp_mmu_page(struct kvm *kvm, u64 *pt)
 
 	trace_kvm_mmu_prepare_zap_page(sp);
 
-	list_del(&sp->link);
-
-	if (sp->lpage_disallowed)
-		unaccount_huge_nx_page(kvm, sp);
+	tdp_mmu_unlink_page(kvm, sp);
 
 	for (i = 0; i < PT64_ENT_PER_PAGE; i++) {
 		old_child_spte = READ_ONCE(*(pt + i));
@@ -705,15 +735,16 @@ int kvm_tdp_mmu_map(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
 
 		if (!is_shadow_present_pte(iter.old_spte)) {
 			sp = alloc_tdp_mmu_page(vcpu, iter.gfn, iter.level);
-			list_add(&sp->link, &vcpu->kvm->arch.tdp_mmu_pages);
 			child_pt = sp->spt;
+
+			tdp_mmu_link_page(vcpu->kvm, sp,
+					  huge_page_disallowed &&
+					  req_level >= iter.level);
+
 			new_spte = make_nonleaf_spte(child_pt,
 						     !shadow_accessed_mask);
 
 			trace_kvm_mmu_get_page(sp, true);
-			if (huge_page_disallowed && req_level >= iter.level)
-				account_huge_nx_page(vcpu->kvm, sp);
-
 			tdp_mmu_set_spte(vcpu->kvm, &iter, new_spte);
 		}
 	}