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

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Message-ID: <20250408112402.181574-7-shivankg@amd.com>
Date: Tue, 8 Apr 2025 11:24:00 +0000
From: Shivank Garg <shivankg@....com>
To: <seanjc@...gle.com>, <david@...hat.com>, <vbabka@...e.cz>,
	<willy@...radead.org>, <akpm@...ux-foundation.org>, <shuah@...nel.org>,
	<pbonzini@...hat.com>
CC: <ackerleytng@...gle.com>, <paul@...l-moore.com>, <jmorris@...ei.org>,
	<serge@...lyn.com>, <pvorel@...e.cz>, <bfoster@...hat.com>,
	<tabba@...gle.com>, <vannapurve@...gle.com>, <chao.gao@...el.com>,
	<bharata@....com>, <nikunj@....com>, <michael.day@....com>,
	<yan.y.zhao@...el.com>, <Neeraj.Upadhyay@....com>, <thomas.lendacky@....com>,
	<michael.roth@....com>, <aik@....com>, <jgg@...dia.com>,
	<kalyazin@...zon.com>, <peterx@...hat.com>, <shivankg@....com>,
	<linux-fsdevel@...r.kernel.org>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>, <linux-security-module@...r.kernel.org>,
	<kvm@...r.kernel.org>, <linux-kselftest@...r.kernel.org>,
	<linux-coco@...ts.linux.dev>
Subject: [PATCH RFC v7 6/8] KVM: guest_memfd: Add slab-allocated inode cache

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 <shivankg@....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