[PATCH RFC V10 5/7] 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 | 69 ++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 67 insertions(+), 2 deletions(-)

diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index 0e93323fc839..d9c23401e770 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -17,6 +17,15 @@ 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.
@@ -389,13 +398,46 @@ static struct file_operations kvm_gmem_fops = {
        .fallocate      = kvm_gmem_fallocate,
 };
 
+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)
 {
+       struct pseudo_fs_context *ctx;
+
        if (!init_pseudo(fc, GUEST_MEMFD_MAGIC))
                return -ENOMEM;
 
        fc->s_iflags |= SB_I_NOEXEC;
        fc->s_iflags |= SB_I_NODEV;
+       ctx = fc->fs_private;
+       ctx->ops = &kvm_gmem_super_operations;
 
        return 0;
 }
@@ -417,17 +459,40 @@ static int kvm_gmem_init_mount(void)
        return 0;
 }
 
+static void kvm_gmem_init_inode(void *foo)
+{
+       struct kvm_gmem_inode_info *info = foo;
+
+       inode_init_once(&info->vfs_inode);
+}
+
 int kvm_gmem_init(struct module *module)
 {
-       kvm_gmem_fops.owner = module;
+       int ret;
+       struct kmem_cache_args args = {
+               .align = 0,
+               .ctor = kvm_gmem_init_inode,
+       };
 
-       return kvm_gmem_init_mount();
+       kvm_gmem_fops.owner = module;
+       kvm_gmem_inode_cachep = kmem_cache_create("kvm_gmem_inode_cache",
+                                                 sizeof(struct 
kvm_gmem_inode_info),
+                                                 &args, SLAB_ACCOUNT);
+       if (!kvm_gmem_inode_cachep)
+               return -ENOMEM;
+       ret = kvm_gmem_init_mount();
+       if (ret) {
+               kmem_cache_destroy(kvm_gmem_inode_cachep);
+               return ret;
+       }
+       return 0;
 }
 
 void kvm_gmem_exit(void)
 {
        kern_unmount(kvm_gmem_mnt);
        kvm_gmem_mnt = NULL;
+       kmem_cache_destroy(kvm_gmem_inode_cachep);
 }
 
 static int kvm_gmem_migrate_folio(struct address_space *mapping,
-- 
2.43.0