[PATCH v12 04/12] KVM: guest_memfd: Add slab-allocated inode cache

Sean Christopherson
2025-10-07T22:14:44Z

From: Shivank Garg <shivankg@amd.com>

Add a dedicated gmem_inode structure and a slab-allocateda 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. Using a dedicated
structure will also allow for additional cleanups, e.g. to track flags in
gmem_inode instead of i_private.

Signed-off-by: Shivank Garg <shivankg@amd.com>
Tested-by: Ashish Kalra <ashish.kalra@amd.com>
[sean: s/kvm_gmem_inode_info/gmem_inode, name init_once()]
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
virt/kvm/guest_memfd.c | 77 +++++++++++++++++++++++++++++++++++++++++-
1 file changed, 76 insertions(+), 1 deletion(-)

diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index 2a580b2bdc9d..cc3b25155726 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -26,6 +26,15 @@ struct gmem_file {
struct list_head entry;
};

+struct gmem_inode {
+ struct inode vfs_inode;
+};
+
+static __always_inline struct gmem_inode *GMEM_I(struct inode *inode)
+{
+ return container_of(inode, struct gmem_inode, vfs_inode);
+}
+
#define kvm_gmem_for_each_file(f, mapping) \
list_for_each_entry(f, &(mapping)->i_private_list, entry)

@@ -833,13 +842,61 @@ long kvm_gmem_populate(struct kvm *kvm, gfn_t start_gfn, void __user *src, long
EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_gmem_populate);
#endif

+static struct kmem_cache *kvm_gmem_inode_cachep;
+
+static void kvm_gmem_init_inode_once(void *__gi)
+{
+ struct gmem_inode *gi = __gi;
+
+ /*
+ * Note! Don't initialize the inode with anything specific to the
+ * guest_memfd instance, or that might be specific to how the inode is
+ * used (from the VFS-layer's perspective). This hook is called only
+ * during the initial slab allocation, i.e. only fields/state that are
+ * idempotent across _all_ use of the inode _object_ can be initialized
+ * at this time!
+ */
+ inode_init_once(&gi->vfs_inode);
+}
+
+static struct inode *kvm_gmem_alloc_inode(struct super_block *sb)
+{
+ struct gmem_inode *gi;
+
+ gi = alloc_inode_sb(sb, kvm_gmem_inode_cachep, GFP_KERNEL);
+ if (!gi)
+ return NULL;
+
+ return &gi->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, 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;
}
@@ -863,13 +920,31 @@ static int kvm_gmem_init_mount(void)

int kvm_gmem_init(struct module *module)
{
+ struct kmem_cache_args args = {
+ .align = 0,
+ .ctor = kvm_gmem_init_inode_once,
+ };
+ int ret;
+
kvm_gmem_fops.owner = module;
+ kvm_gmem_inode_cachep = kmem_cache_create("kvm_gmem_inode_cache",
+ sizeof(struct gmem_inode),
+ &args, SLAB_ACCOUNT);
+ if (!kvm_gmem_inode_cachep)
+ return -ENOMEM;

- return kvm_gmem_init_mount();
+ 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;
+ rcu_barrier();
+ kmem_cache_destroy(kvm_gmem_inode_cachep);
}
--
2.51.0.710.ga91ca5db03-goog