Add 'notifier' to memslot to make it a memfile_notifier node and then
register it to memory backing store via memfile_register_notifier() when
memslot gets created. When memslot is deleted, do the reverse with
memfile_unregister_notifier(). Note each KVM memslot can be registered
to different memory backing stores (or the same backing store but at
different offset) independently.

Signed-off-by: Yu Zhang <redacted>
Signed-off-by: Chao Peng <redacted>
---
 include/linux/kvm_host.h |  1 +
 virt/kvm/kvm_main.c      | 75 ++++++++++++++++++++++++++++++++++++----
 2 files changed, 70 insertions(+), 6 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 6e1d770d6bf8..9b175aeca63f 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h

@@ -567,6 +567,7 @@ struct kvm_memory_slot {
 	struct file *private_file;
 	loff_t private_offset;
 	struct memfile_pfn_ops *pfn_ops;
+	struct memfile_notifier notifier;
 };
 
 static inline bool kvm_slot_is_private(const struct kvm_memory_slot *slot)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index d11a2628b548..67349421eae3 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c

@@ -840,6 +840,37 @@ static int kvm_init_mmu_notifier(struct kvm *kvm)
 
 #endif /* CONFIG_MMU_NOTIFIER && KVM_ARCH_WANT_MMU_NOTIFIER */
 
+#ifdef CONFIG_MEMFILE_NOTIFIER
+static inline int kvm_memfile_register(struct kvm_memory_slot *slot)

+	return -EOPNOTSUPP;
+}
+
+static inline void kvm_memfile_unregister(struct kvm_memory_slot *slot)
+{
+}
+
+#endif /* CONFIG_MEMFILE_NOTIFIER */
+
 #ifdef CONFIG_HAVE_KVM_PM_NOTIFIER
 static int kvm_pm_notifier_call(struct notifier_block *bl,
 				unsigned long state,

@@ -884,6 +915,9 @@ static void kvm_destroy_dirty_bitmap(struct kvm_memory_slot *memslot)
 /* This does not remove the slot from struct kvm_memslots data structures */
 static void kvm_free_memslot(struct kvm *kvm, struct kvm_memory_slot *slot)
 {
+	if (slot->flags & KVM_MEM_PRIVATE)
+		kvm_memfile_unregister(slot);

+
 	kvm_destroy_dirty_bitmap(slot);
 
 	kvm_arch_free_memslot(kvm, slot);

@@ -1738,6 +1772,12 @@ static int kvm_set_memslot(struct kvm *kvm,
 		kvm_invalidate_memslot(kvm, old, invalid_slot);
 	}
 
+	if (new->flags & KVM_MEM_PRIVATE && change == KVM_MR_CREATE) {
+		r = kvm_memfile_register(new);
+		if (r)
+			return r;
+	}

+
 	r = kvm_prepare_memory_region(kvm, old, new, change);
 	if (r) {
 		/*

@@ -1752,6 +1792,10 @@ static int kvm_set_memslot(struct kvm *kvm,
 		} else {
 			mutex_unlock(&kvm->slots_arch_lock);
 		}
+
+		if (new->flags & KVM_MEM_PRIVATE && change == KVM_MR_CREATE)
+			kvm_memfile_unregister(new);
+
 		return r;
 	}
 

@@ -1817,6 +1861,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
 	enum kvm_mr_change change;
 	unsigned long npages;
 	gfn_t base_gfn;
+	struct file *file = NULL;

 	int as_id, id;
 	int r;
 

@@ -1890,14 +1935,24 @@ int __kvm_set_memory_region(struct kvm *kvm,
 			return 0;
 	}
 
+	if (mem->flags & KVM_MEM_PRIVATE) {
+		file = fdget(region_ext->private_fd).file;

+		if (!file)
+			return -EINVAL;
+	}
+
 	if ((change == KVM_MR_CREATE || change == KVM_MR_MOVE) &&
-	    kvm_check_memslot_overlap(slots, id, base_gfn, base_gfn + npages))
-		return -EEXIST;
+	    kvm_check_memslot_overlap(slots, id, base_gfn, base_gfn + npages)) {
+		r = -EEXIST;
+		goto out;
+	}
 
 	/* Allocate a slot that will persist in the memslot. */
 	new = kzalloc(sizeof(*new), GFP_KERNEL_ACCOUNT);
-	if (!new)
-		return -ENOMEM;
+	if (!new) {
+		r = -ENOMEM;
+		goto out;
+	}
 
 	new->as_id = as_id;
 	new->id = id;

@@ -1905,10 +1960,18 @@ int __kvm_set_memory_region(struct kvm *kvm,
 	new->npages = npages;
 	new->flags = mem->flags;
 	new->userspace_addr = mem->userspace_addr;
+	new->private_file = file;
+	new->private_offset = mem->flags & KVM_MEM_PRIVATE ?
+			      region_ext->private_offset : 0;