[PATCH v2 20/27] KVM: x86/mmu: Use page-track notifiers iff there are external users

[Sean Christopherson]

Disable the page-track notifier code at compile time if there are no
external users, i.e. if CONFIG_KVM_EXTERNAL_WRITE_TRACKING=n.  KVM itself
now hooks emulated writes directly instead of relying on the page-track
mechanism.

Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
 arch/x86/include/asm/kvm_host.h       |  2 ++
 arch/x86/include/asm/kvm_page_track.h |  2 ++
 arch/x86/kvm/mmu/page_track.c         |  9 ++++-----
 arch/x86/kvm/mmu/page_track.h         | 29 +++++++++++++++++++++++----
 4 files changed, 33 insertions(+), 9 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 1a4225237564..a3423711e403 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1265,7 +1265,9 @@ struct kvm_arch {
 	 * create an NX huge page (without hanging the guest).
 	 */
 	struct list_head possible_nx_huge_pages;
+#ifdef CONFIG_KVM_EXTERNAL_WRITE_TRACKING
 	struct kvm_page_track_notifier_head track_notifier_head;
+#endif
 	/*
 	 * Protects marking pages unsync during page faults, as TDP MMU page
 	 * faults only take mmu_lock for read.  For simplicity, the unsync
diff --git a/arch/x86/include/asm/kvm_page_track.h b/arch/x86/include/asm/kvm_page_track.h
index deece45936a5..53c2adb25a07 100644
--- a/arch/x86/include/asm/kvm_page_track.h
+++ b/arch/x86/include/asm/kvm_page_track.h
@@ -55,6 +55,7 @@ void kvm_slot_page_track_remove_page(struct kvm *kvm,
 				     struct kvm_memory_slot *slot, gfn_t gfn,
 				     enum kvm_page_track_mode mode);
 
+#ifdef CONFIG_KVM_EXTERNAL_WRITE_TRACKING
 enum pg_level kvm_page_track_max_mapping_level(struct kvm *kvm, gfn_t gfn,
 					       enum pg_level max_level);
 
@@ -64,5 +65,6 @@ kvm_page_track_register_notifier(struct kvm *kvm,
 void
 kvm_page_track_unregister_notifier(struct kvm *kvm,
 				   struct kvm_page_track_notifier_node *n);
+#endif /* CONFIG_KVM_EXTERNAL_WRITE_TRACKING */
 
 #endif
diff --git a/arch/x86/kvm/mmu/page_track.c b/arch/x86/kvm/mmu/page_track.c
index a21200df515d..619ec8e5fd32 100644
--- a/arch/x86/kvm/mmu/page_track.c
+++ b/arch/x86/kvm/mmu/page_track.c
@@ -194,6 +194,7 @@ bool kvm_slot_page_track_is_active(struct kvm *kvm,
 	return !!READ_ONCE(slot->arch.gfn_track[mode][index]);
 }
 
+#ifdef CONFIG_KVM_EXTERNAL_WRITE_TRACKING
 void kvm_page_track_cleanup(struct kvm *kvm)
 {
 	struct kvm_page_track_notifier_head *head;
@@ -255,14 +256,13 @@ EXPORT_SYMBOL_GPL(kvm_page_track_unregister_notifier);
  * The node should figure out if the written page is the one that node is
  * interested in by itself.
  */
-void kvm_page_track_write(struct kvm_vcpu *vcpu, gpa_t gpa, const u8 *new,
-			  int bytes)
+void __kvm_page_track_write(struct kvm *kvm, gpa_t gpa, const u8 *new, int bytes)
 {
 	struct kvm_page_track_notifier_head *head;
 	struct kvm_page_track_notifier_node *n;
 	int idx;
 
-	head = &vcpu->kvm->arch.track_notifier_head;
+	head = &kvm->arch.track_notifier_head;
 
 	if (hlist_empty(&head->track_notifier_list))
 		return;
@@ -273,8 +273,6 @@ void kvm_page_track_write(struct kvm_vcpu *vcpu, gpa_t gpa, const u8 *new,
 		if (n->track_write)
 			n->track_write(gpa, new, bytes, n);
 	srcu_read_unlock(&head->track_srcu, idx);
-
-	kvm_mmu_track_write(vcpu, gpa, new, bytes);
 }
 
 /*
@@ -317,3 +315,4 @@ enum pg_level kvm_page_track_max_mapping_level(struct kvm *kvm, gfn_t gfn,
 	return max_level;
 }
 EXPORT_SYMBOL_GPL(kvm_page_track_max_mapping_level);
+#endif
diff --git a/arch/x86/kvm/mmu/page_track.h b/arch/x86/kvm/mmu/page_track.h
index 89712f123ad3..931b26b8fc8f 100644
--- a/arch/x86/kvm/mmu/page_track.h
+++ b/arch/x86/kvm/mmu/page_track.h
@@ -6,8 +6,6 @@
 
 #include <asm/kvm_page_track.h>
 
-int kvm_page_track_init(struct kvm *kvm);
-void kvm_page_track_cleanup(struct kvm *kvm);
 
 bool kvm_page_track_write_tracking_enabled(struct kvm *kvm);
 int kvm_page_track_write_tracking_alloc(struct kvm_memory_slot *slot);
@@ -21,13 +19,36 @@ bool kvm_slot_page_track_is_active(struct kvm *kvm,
 				   const struct kvm_memory_slot *slot,
 				   gfn_t gfn, enum kvm_page_track_mode mode);
 
-void kvm_page_track_write(struct kvm_vcpu *vcpu, gpa_t gpa, const u8 *new,
-			  int bytes);
+#ifdef CONFIG_KVM_EXTERNAL_WRITE_TRACKING
+int kvm_page_track_init(struct kvm *kvm);
+void kvm_page_track_cleanup(struct kvm *kvm);
+
+void __kvm_page_track_write(struct kvm *kvm, gpa_t gpa, const u8 *new, int bytes);
 void kvm_page_track_delete_slot(struct kvm *kvm, struct kvm_memory_slot *slot);
 
 static inline bool kvm_page_track_has_external_user(struct kvm *kvm)
 {
 	return hlist_empty(&kvm->arch.track_notifier_head.track_notifier_list);
 }
+#else
+static inline int kvm_page_track_init(struct kvm *kvm) { return 0; }
+static inline void kvm_page_track_cleanup(struct kvm *kvm) { }
+
+static inline void __kvm_page_track_write(struct kvm *kvm, gpa_t gpa,
+					  const u8 *new, int bytes) { }
+static inline void kvm_page_track_delete_slot(struct kvm *kvm,
+					      struct kvm_memory_slot *slot) { }
+
+static inline bool kvm_page_track_has_external_user(struct kvm *kvm) { return false; }
+
+#endif /* CONFIG_KVM_EXTERNAL_WRITE_TRACKING */
+
+static inline void kvm_page_track_write(struct kvm_vcpu *vcpu, gpa_t gpa,
+					const u8 *new, int bytes)
+{
+	__kvm_page_track_write(vcpu->kvm, gpa, new, bytes);
+
+	kvm_mmu_track_write(vcpu, gpa, new, bytes);
+}
 
 #endif /* __KVM_X86_PAGE_TRACK_H */
-- 
2.40.0.rc1.284.g88254d51c5-goog