[PATCH RFC v7 6/8] KVM: guest_memfd: Add slab-allocated inode cache

[Shivank Garg]

Add dedicated inode structure (kvm_gmem_inode_info) and slab-allocated
inode cache for guest memory backing, similar to how shmem handles inodes.

This adds the necessary allocation/destruction functions and prepares
for upcoming guest_memfd NUMA policy support changes.

Signed-off-by: Shivank Garg <shiva...@amd.com>
---
 virt/kvm/guest_memfd.c | 52 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 52 insertions(+)

diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index 002328569c9e..0ccbb152483a 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -18,6 +18,15 @@ struct kvm_gmem {
        struct list_head entry;
 };
 
+struct kvm_gmem_inode_info {
+       struct inode vfs_inode;
+};
+
+static inline struct kvm_gmem_inode_info *KVM_GMEM_I(struct inode *inode)
+{
+       return container_of(inode, struct kvm_gmem_inode_info, vfs_inode);
+}
+
 /**
  * folio_file_pfn - like folio_file_page, but return a pfn.
  * @folio: The folio which contains this index.
@@ -317,8 +326,34 @@ static pgoff_t kvm_gmem_get_index(struct kvm_memory_slot 
*slot, gfn_t gfn)
        return gfn - slot->base_gfn + slot->gmem.pgoff;
 }
 
+static struct kmem_cache *kvm_gmem_inode_cachep;
+
+static struct inode *kvm_gmem_alloc_inode(struct super_block *sb)
+{
+       struct kvm_gmem_inode_info *info;
+
+       info = alloc_inode_sb(sb, kvm_gmem_inode_cachep, GFP_KERNEL);
+       if (!info)
+               return NULL;
+
+       return &info->vfs_inode;
+}
+
+static void kvm_gmem_destroy_inode(struct inode *inode)
+{
+
+}
+
+static void kvm_gmem_free_inode(struct inode *inode)
+{
+       kmem_cache_free(kvm_gmem_inode_cachep, KVM_GMEM_I(inode));
+}
+
 static const struct super_operations kvm_gmem_super_operations = {
        .statfs         = simple_statfs,
+       .alloc_inode    = kvm_gmem_alloc_inode,
+       .destroy_inode  = kvm_gmem_destroy_inode,
+       .free_inode     = kvm_gmem_free_inode,
 };
 
 static int kvm_gmem_init_fs_context(struct fs_context *fc)
@@ -355,16 +390,33 @@ static struct file_operations kvm_gmem_fops = {
        .fallocate      = kvm_gmem_fallocate,
 };
 
+static void kvm_gmem_init_inode(void *foo)
+{
+       struct kvm_gmem_inode_info *info = foo;
+
+       inode_init_once(&info->vfs_inode);
+}
+
+static void kvm_gmem_init_inodecache(void)
+{
+       kvm_gmem_inode_cachep = kmem_cache_create("kvm_gmem_inode_cache",
+                                                 sizeof(struct 
kvm_gmem_inode_info),
+                                                 0, SLAB_ACCOUNT,
+                                                 kvm_gmem_init_inode);
+}
+
 void kvm_gmem_init(struct module *module)
 {
        kvm_gmem_fops.owner = module;
 
+       kvm_gmem_init_inodecache();
        kvm_gmem_init_mount();
 }
 
 void kvm_gmem_exit(void)
 {
        kern_unmount(kvm_gmem_mnt);
+       kmem_cache_destroy(kvm_gmem_inode_cachep);
 }
 
 static int kvm_gmem_migrate_folio(struct address_space *mapping,
-- 
2.34.1