KVM: page track: add notifier support

Notifier list is introduced so that any node wants to receive the track
event can register to the list

Two APIs are introduced here:
- kvm_page_track_register_notifier(): register the notifier to receive
  track event

- kvm_page_track_unregister_notifier(): stop receiving track event by
  unregister the notifier

The callback, node->track_write() is called when a write access on the
write tracked page happens

Signed-off-by: Xiao Guangrong <guangrong.xiao@linux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

4 files changed, 114 insertions, 0 deletions

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index e2fc5c0ec86a..eb68e6aca0cf 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -704,6 +704,7 @@ struct kvm_arch {
          */
         struct list_head active_mmu_pages;
         struct list_head zapped_obsolete_pages;
+        struct kvm_page_track_notifier_head track_notifier_head;
 
         struct list_head assigned_dev_head;
         struct iommu_domain *iommu_domain;
diff --git a/arch/x86/include/asm/kvm_page_track.h b/arch/x86/include/asm/kvm_page_track.h
index 5f16e2864e73..c2b8d24a235c 100644
--- a/arch/x86/include/asm/kvm_page_track.h
+++ b/arch/x86/include/asm/kvm_page_track.h
@@ -6,6 +6,36 @@ enum kvm_page_track_mode {
         KVM_PAGE_TRACK_MAX,
 };
 
+/*
+ * The notifier represented by @kvm_page_track_notifier_node is linked into
+ * the head which will be notified when guest is triggering the track event.
+ *
+ * Write access on the head is protected by kvm->mmu_lock, read access
+ * is protected by track_srcu.
+ */
+struct kvm_page_track_notifier_head {
+        struct srcu_struct track_srcu;
+        struct hlist_head track_notifier_list;
+};
+
+struct kvm_page_track_notifier_node {
+        struct hlist_node node;
+
+        /*
+         * It is called when guest is writing the write-tracked page
+         * and write emulation is finished at that time.
+         *
+         * @vcpu: the vcpu where the write access happened.
+         * @gpa: the physical address written by guest.
+         * @new: the data was written to the address.
+         * @bytes: the written length.
+         */
+        void (*track_write)(struct kvm_vcpu *vcpu, gpa_t gpa, const u8 *new,
+                            int bytes);
+};
+
+void kvm_page_track_init(struct kvm *kvm);
+
 void kvm_page_track_free_memslot(struct kvm_memory_slot *free,
                                  struct kvm_memory_slot *dont);
 int kvm_page_track_create_memslot(struct kvm_memory_slot *slot,
@@ -19,4 +49,13 @@ void kvm_slot_page_track_remove_page(struct kvm *kvm,
                                      enum kvm_page_track_mode mode);
 bool kvm_page_track_is_active(struct kvm_vcpu *vcpu, gfn_t gfn,
                               enum kvm_page_track_mode mode);
+
+void
+kvm_page_track_register_notifier(struct kvm *kvm,
+                                 struct kvm_page_track_notifier_node *n);
+void
+kvm_page_track_unregister_notifier(struct kvm *kvm,
+                                   struct kvm_page_track_notifier_node *n);
+void kvm_page_track_write(struct kvm_vcpu *vcpu, gpa_t gpa, const u8 *new,
+                          int bytes);
 #endif
diff --git a/arch/x86/kvm/page_track.c b/arch/x86/kvm/page_track.c
index f127f6d04fa1..11f76436f74f 100644
--- a/arch/x86/kvm/page_track.c
+++ b/arch/x86/kvm/page_track.c
@@ -150,3 +150,73 @@ bool kvm_page_track_is_active(struct kvm_vcpu *vcpu, gfn_t gfn,
 
         return !!ACCESS_ONCE(slot->arch.gfn_track[mode][index]);
 }
+
+void kvm_page_track_init(struct kvm *kvm)
+{
+        struct kvm_page_track_notifier_head *head;
+
+        head = &kvm->arch.track_notifier_head;
+        init_srcu_struct(&head->track_srcu);
+        INIT_HLIST_HEAD(&head->track_notifier_list);
+}
+
+/*
+ * register the notifier so that event interception for the tracked guest
+ * pages can be received.
+ */
+void
+kvm_page_track_register_notifier(struct kvm *kvm,
+                                 struct kvm_page_track_notifier_node *n)
+{
+        struct kvm_page_track_notifier_head *head;
+
+        head = &kvm->arch.track_notifier_head;
+
+        spin_lock(&kvm->mmu_lock);
+        hlist_add_head_rcu(&n->node, &head->track_notifier_list);
+        spin_unlock(&kvm->mmu_lock);
+}
+
+/*
+ * stop receiving the event interception. It is the opposed operation of
+ * kvm_page_track_register_notifier().
+ */
+void
+kvm_page_track_unregister_notifier(struct kvm *kvm,
+                                   struct kvm_page_track_notifier_node *n)
+{
+        struct kvm_page_track_notifier_head *head;
+
+        head = &kvm->arch.track_notifier_head;
+
+        spin_lock(&kvm->mmu_lock);
+        hlist_del_rcu(&n->node);
+        spin_unlock(&kvm->mmu_lock);
+        synchronize_srcu(&head->track_srcu);
+}
+
+/*
+ * Notify the node that write access is intercepted and write emulation is
+ * finished at this time.
+ *
+ * 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)
+{
+        struct kvm_page_track_notifier_head *head;
+        struct kvm_page_track_notifier_node *n;
+        int idx;
+
+        head = &vcpu->kvm->arch.track_notifier_head;
+
+        if (hlist_empty(&head->track_notifier_list))
+                return;
+
+        idx = srcu_read_lock(&head->track_srcu);
+        hlist_for_each_entry_rcu(n, &head->track_notifier_list, node)
+                if (n->track_write)
+                        n->track_write(vcpu, gpa, new, bytes);
+        srcu_read_unlock(&head->track_srcu, idx);
+}
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 7b4cfea09deb..b81c14ef1e1d 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4346,6 +4346,7 @@ int emulator_write_phys(struct kvm_vcpu *vcpu, gpa_t gpa,
         if (ret < 0)
                 return 0;
         kvm_mmu_pte_write(vcpu, gpa, val, bytes);
+        kvm_page_track_write(vcpu, gpa, val, bytes);
         return 1;
 }
 
@@ -4604,6 +4605,7 @@ static int emulator_cmpxchg_emulated(struct x86_emulate_ctxt *ctxt,
 
         kvm_vcpu_mark_page_dirty(vcpu, gpa >> PAGE_SHIFT);
         kvm_mmu_pte_write(vcpu, gpa, new, bytes);
+        kvm_page_track_write(vcpu, gpa, new, bytes);
 
         return X86EMUL_CONTINUE;
 
@@ -7724,6 +7726,8 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
         INIT_DELAYED_WORK(&kvm->arch.kvmclock_update_work, kvmclock_update_fn);
         INIT_DELAYED_WORK(&kvm->arch.kvmclock_sync_work, kvmclock_sync_fn);
 
+        kvm_page_track_init(kvm);
+
         return 0;
 }