[PATCH v4 10/12] KVM: Register private memslot to memory backing store

[Chao Peng]

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 <yu.c.zhang@linux.intel.com>
Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
---
 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 927e7f44a02a..667efe839767 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -462,6 +462,7 @@ 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 ecf94e2548f7..6b78ddef7880 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -846,6 +846,37 @@ 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 memfile_register_notifier(file_inode(slot->private_file),
+                                        &slot->notifier,
+                                        &slot->pfn_ops);
+}
+
+static inline void kvm_memfile_unregister(struct kvm_memory_slot *slot)
+{
+       if (slot->private_file) {
+               memfile_unregister_notifier(file_inode(slot->private_file),
+                                           &slot->notifier);
+               fput(slot->private_file);
+               slot->private_file = NULL;
+       }
+}
+
+#else /* !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,
@@ -890,6 +921,9 @@ 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);
@@ -1744,6 +1778,12 @@ 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) {
                /*
@@ -1758,6 +1798,10 @@ 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;
        }
 
@@ -1823,6 +1867,7 @@ 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;
 
@@ -1896,14 +1941,24 @@ 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;
@@ -1911,10 +1966,18 @@ 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;
 
        r = kvm_set_memslot(kvm, old, new, change);
-       if (r)
-               kfree(new);
+       if (!r)
+               return r;
+
+       kfree(new);
+out:
+       if (file)
+               fput(file);
        return r;
 }
 EXPORT_SYMBOL_GPL(__kvm_set_memory_region);
-- 
2.17.1