[PATCH] KVM: guest_memfd: Refactor kvm_gmem into inode->i_private

[isaku . yamahata]

From: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>

Refactor guest_memfd to use inode->i_private to store info about kvm_gmem.
Currently it is stored in the following way.
- flags in inode->i_private
- struct kvm_gmem in file->private_data
- struct kvm_gmem in linked linst in inode->i_mapping->private_list
  And this list has single entry.

The relationship between struct file, struct inode and struct kvm_gmem is
1:1, not 1:many. Consolidate related info in one place.
- Move flags into struct kvm_gmem
- Store struct kvm_gmem in inode->i_private
- Don't use file->private_data
- Don't use inode->i_mapping_private_list
- Introduce a helper conversion function from inode to kvm_gmem

Signed-off-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
---
 virt/kvm/guest_memfd.c | 53 ++++++++++++++++++------------------------
 1 file changed, 23 insertions(+), 30 deletions(-)

diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index 4f3a313f5532..66dd9b55e85c 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -14,14 +14,19 @@ static struct vfsmount *kvm_gmem_mnt;
 struct kvm_gmem {
 	struct kvm *kvm;
 	struct xarray bindings;
-	struct list_head entry;
+	unsigned long flags;
 };
 
+static struct kvm_gmem *to_gmem(struct inode *inode)
+{
+	return inode->i_private;
+}
+
 static struct folio *kvm_gmem_get_huge_folio(struct inode *inode, pgoff_t index)
 {
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 	unsigned long huge_index = round_down(index, HPAGE_PMD_NR);
-	unsigned long flags = (unsigned long)inode->i_private;
+	unsigned long flags = to_gmem(inode)->flags;
 	struct address_space *mapping  = inode->i_mapping;
 	gfp_t gfp = mapping_gfp_mask(mapping);
 	struct folio *folio;
@@ -134,26 +139,22 @@ static void kvm_gmem_invalidate_end(struct kvm_gmem *gmem, pgoff_t start,
 
 static long kvm_gmem_punch_hole(struct inode *inode, loff_t offset, loff_t len)
 {
-	struct list_head *gmem_list = &inode->i_mapping->private_list;
+	struct address_space *mapping = inode->i_mapping;
+	struct kvm_gmem *gmem = to_gmem(inode);
 	pgoff_t start = offset >> PAGE_SHIFT;
 	pgoff_t end = (offset + len) >> PAGE_SHIFT;
-	struct kvm_gmem *gmem;
 
 	/*
 	 * Bindings must stable across invalidation to ensure the start+end
 	 * are balanced.
 	 */
-	filemap_invalidate_lock(inode->i_mapping);
-
-	list_for_each_entry(gmem, gmem_list, entry)
-		kvm_gmem_invalidate_begin(gmem, start, end);
+	filemap_invalidate_lock(mapping);
+	kvm_gmem_invalidate_begin(gmem, start, end);
 
 	truncate_inode_pages_range(inode->i_mapping, offset, offset + len - 1);
 
-	list_for_each_entry(gmem, gmem_list, entry)
-		kvm_gmem_invalidate_end(gmem, start, end);
-
-	filemap_invalidate_unlock(inode->i_mapping);
+	kvm_gmem_invalidate_end(gmem, start, end);
+	filemap_invalidate_unlock(mapping);
 
 	return 0;
 }
@@ -231,7 +232,7 @@ 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 = file->private_data;
+	struct kvm_gmem *gmem = to_gmem(inode);
 	struct kvm_memory_slot *slot;
 	struct kvm *kvm = gmem->kvm;
 	unsigned long index;
@@ -260,8 +261,6 @@ static int kvm_gmem_release(struct inode *inode, struct file *file)
 	kvm_gmem_invalidate_begin(gmem, 0, -1ul);
 	kvm_gmem_invalidate_end(gmem, 0, -1ul);
 
-	list_del(&gmem->entry);
-
 	filemap_invalidate_unlock(inode->i_mapping);
 
 	mutex_unlock(&kvm->slots_lock);
@@ -305,8 +304,7 @@ static int kvm_gmem_migrate_folio(struct address_space *mapping,
 
 static int kvm_gmem_error_page(struct address_space *mapping, struct page *page)
 {
-	struct list_head *gmem_list = &mapping->private_list;
-	struct kvm_gmem *gmem;
+	struct kvm_gmem *gmem = to_gmem(mapping->host);
 	pgoff_t start, end;
 
 	filemap_invalidate_lock_shared(mapping);
@@ -314,8 +312,7 @@ static int kvm_gmem_error_page(struct address_space *mapping, struct page *page)
 	start = page->index;
 	end = start + thp_nr_pages(page);
 
-	list_for_each_entry(gmem, gmem_list, entry)
-		kvm_gmem_invalidate_begin(gmem, start, end);
+	kvm_gmem_invalidate_begin(gmem, start, end);
 
 	/*
 	 * Do not truncate the range, what action is taken in response to the
@@ -326,8 +323,7 @@ static int kvm_gmem_error_page(struct address_space *mapping, struct page *page)
 	 * error to userspace.
 	 */
 
-	list_for_each_entry(gmem, gmem_list, entry)
-		kvm_gmem_invalidate_end(gmem, start, end);
+	kvm_gmem_invalidate_end(gmem, start, end);
 
 	filemap_invalidate_unlock_shared(mapping);
 
@@ -382,7 +378,6 @@ static int __kvm_gmem_create(struct kvm *kvm, loff_t size, u64 flags,
 	if (err)
 		goto err_inode;
 
-	inode->i_private = (void *)(unsigned long)flags;
 	inode->i_op = &kvm_gmem_iops;
 	inode->i_mapping->a_ops = &kvm_gmem_aops;
 	inode->i_mode |= S_IFREG;
@@ -417,10 +412,9 @@ static int __kvm_gmem_create(struct kvm *kvm, loff_t size, u64 flags,
 	kvm_get_kvm(kvm);
 	gmem->kvm = kvm;
 	xa_init(&gmem->bindings);
+	gmem->flags = flags;
 
-	file->private_data = gmem;
-
-	list_add(&gmem->entry, &inode->i_mapping->private_list);
+	inode->i_private = gmem;
 
 	fd_install(fd, file);
 	return fd;
@@ -476,12 +470,11 @@ int kvm_gmem_bind(struct kvm *kvm, struct kvm_memory_slot *slot,
 	if (file->f_op != &kvm_gmem_fops)
 		goto err;
 
-	gmem = file->private_data;
+	inode = file_inode(file);
+	gmem = to_gmem(inode);
 	if (gmem->kvm != kvm)
 		goto err;
 
-	inode = file_inode(file);
-
 	if (offset < 0 || !PAGE_ALIGNED(offset))
 		return -EINVAL;
 
@@ -538,7 +531,7 @@ void kvm_gmem_unbind(struct kvm_memory_slot *slot)
 	if (!file)
 		return;
 
-	gmem = file->private_data;
+	gmem = to_gmem(file_inode(file));
 
 	filemap_invalidate_lock(file->f_mapping);
 	xa_store_range(&gmem->bindings, start, end - 1, NULL, GFP_KERNEL);
@@ -563,7 +556,7 @@ int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot,
 	if (!file)
 		return -EFAULT;
 
-	gmem = file->private_data;
+	gmem = to_gmem(file_inode(file));
 
 	if (WARN_ON_ONCE(xa_load(&gmem->bindings, index) != slot)) {
 		r = -EIO;
-- 
2.25.1