[RFC PATCH 14/19] KVM: guest_mem: Refactor cleanup to separate inode and file cleanup

[Ackerley Tng]

Cleanup in kvm_gmem_release() should be the reverse of
kvm_gmem_create_file().

Cleanup in kvm_gmem_evict_inode() should be the reverse of
kvm_gmem_create_inode().

Signed-off-by: Ackerley Tng <ackerleytng@google.com>
---
 virt/kvm/guest_mem.c | 105 +++++++++++++++++++++++++++++--------------
 1 file changed, 71 insertions(+), 34 deletions(-)

diff --git a/virt/kvm/guest_mem.c b/virt/kvm/guest_mem.c
index 2f69ef666871..13253af40be6 100644
--- a/virt/kvm/guest_mem.c
+++ b/virt/kvm/guest_mem.c
@@ -247,42 +247,13 @@ static long kvm_gmem_fallocate(struct file *file, int 
mode, loff_t offset,
 
 static int kvm_gmem_release(struct inode *inode, struct file *file)
 {
-       struct kvm_gmem *gmem = inode->i_mapping->private_data;
-       struct kvm_memory_slot *slot;
-       struct kvm *kvm = gmem->kvm;
-       unsigned long index;
-
        /*
-        * Prevent concurrent attempts to *unbind* a memslot.  This is the last
-        * reference to the file and thus no new bindings can be created, but
-        * deferencing the slot for existing bindings needs to be protected
-        * against memslot updates, specifically so that unbind doesn't race
-        * and free the memslot (kvm_gmem_get_file() will return NULL).
+        * This is called when the last reference to the file is released. Only
+        * clean up file-related stuff. struct kvm_gmem is also referred to in
+        * the inode, so clean that up in kvm_gmem_evict_inode().
         */
-       mutex_lock(&kvm->slots_lock);
-
-       xa_for_each(&gmem->bindings, index, slot)
-               rcu_assign_pointer(slot->gmem.file, NULL);
-
-       synchronize_rcu();
-
-       /*
-        * All in-flight operations are gone and new bindings can be created.
-        * Free the backing memory, and more importantly, zap all SPTEs that
-        * pointed at this file.
-        */
-       kvm_gmem_invalidate_begin(kvm, gmem, 0, -1ul);
-       truncate_inode_pages_final(file->f_mapping);
-       kvm_gmem_invalidate_end(kvm, gmem, 0, -1ul);
-
-       mutex_unlock(&kvm->slots_lock);
-
-       WARN_ON_ONCE(!(mapping_empty(file->f_mapping)));
-
-       xa_destroy(&gmem->bindings);
-       kfree(gmem);
-
-       kvm_put_kvm(kvm);
+       file->f_mapping = NULL;
+       file->private_data = NULL;
 
        return 0;
 }
@@ -603,11 +574,77 @@ int kvm_gmem_get_pfn(struct kvm *kvm, struct 
kvm_memory_slot *slot,
 }
 EXPORT_SYMBOL_GPL(kvm_gmem_get_pfn);
 
+static void kvm_gmem_evict_inode(struct inode *inode)
+{
+       struct kvm_gmem *gmem = inode->i_mapping->private_data;
+       struct kvm_memory_slot *slot;
+       struct kvm *kvm;
+       unsigned long index;
+
+       /*
+        * If iput() was called before inode is completely set up due to some
+        * error in kvm_gmem_create_inode(), gmem will be NULL.
+        */
+       if (!gmem)
+               goto basic_cleanup;
+
+       kvm = gmem->kvm;
+
+       /*
+        * Prevent concurrent attempts to *unbind* a memslot.  This is the last
+        * reference to the file and thus no new bindings can be created, but
+        * deferencing the slot for existing bindings needs to be protected
+        * against memslot updates, specifically so that unbind doesn't race
+        * and free the memslot (kvm_gmem_get_file() will return NULL).
+        */
+       mutex_lock(&kvm->slots_lock);
+
+       xa_for_each(&gmem->bindings, index, slot)
+               rcu_assign_pointer(slot->gmem.file, NULL);
+
+       synchronize_rcu();
+
+       /*
+        * All in-flight operations are gone and new bindings can be created.
+        * Free the backing memory, and more importantly, zap all SPTEs that
+        * pointed at this file.
+        */
+       kvm_gmem_invalidate_begin(kvm, gmem, 0, -1ul);
+       truncate_inode_pages_final(inode->i_mapping);
+       kvm_gmem_invalidate_end(kvm, gmem, 0, -1ul);
+
+       mutex_unlock(&kvm->slots_lock);
+
+       WARN_ON_ONCE(!(mapping_empty(inode->i_mapping)));
+
+       xa_destroy(&gmem->bindings);
+       kfree(gmem);
+
+       kvm_put_kvm(kvm);
+
+basic_cleanup:
+       clear_inode(inode);
+}
+
+static const struct super_operations kvm_gmem_super_operations = {
+       /*
+        * TODO update statfs handler for kvm_gmem. What should the statfs
+        * handler return?
+        */
+       .statfs         = simple_statfs,
+       .evict_inode    = kvm_gmem_evict_inode,
+};
+
 static int kvm_gmem_init_fs_context(struct fs_context *fc)
 {
+       struct pseudo_fs_context *ctx;
+
        if (!init_pseudo(fc, GUEST_MEMORY_MAGIC))
                return -ENOMEM;
 
+       ctx = fc->fs_private;
+       ctx->ops = &kvm_gmem_super_operations;
+
        return 0;
 }
 
-- 
2.41.0.rc0.172.g3f132b7071-goog