Hi Fuad,
On 1/18/25 2:29 AM, Fuad Tabba wrote:
From: Ackerley Tng <ackerleytng@xxxxxxxxxx>
Using guest mem inodes allows us to store metadata for the backing
memory on the inode. Metadata will be added in a later patch to
support HugeTLB pages.
Metadata about backing memory should not be stored on the file, since
the file represents a guest_memfd's binding with a struct kvm, and
metadata about backing memory is not unique to a specific binding and
struct kvm.
Signed-off-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>
Signed-off-by: Fuad Tabba <tabba@xxxxxxxxxx>
---
include/uapi/linux/magic.h | 1 +
virt/kvm/guest_memfd.c | 119 ++++++++++++++++++++++++++++++-------
2 files changed, 100 insertions(+), 20 deletions(-)
diff --git a/include/uapi/linux/magic.h b/include/uapi/linux/magic.h
index bb575f3ab45e..169dba2a6920 100644
--- a/include/uapi/linux/magic.h
+++ b/include/uapi/linux/magic.h
@@ -103,5 +103,6 @@
#define DEVMEM_MAGIC 0x454d444d /* "DMEM" */
#define SECRETMEM_MAGIC 0x5345434d /* "SECM" */
#define PID_FS_MAGIC 0x50494446 /* "PIDF" */
+#define GUEST_MEMORY_MAGIC 0x474d454d /* "GMEM" */
#endif /* __LINUX_MAGIC_H__ */
diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index 47a9f68f7b24..198554b1f0b5 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -1,12 +1,17 @@
// SPDX-License-Identifier: GPL-2.0
+#include <linux/fs.h>
+#include <linux/mount.h>
This can be dropped since "linux/mount.h" has been included to "linux/fs.h".
#include <linux/backing-dev.h>
#include <linux/falloc.h>
#include <linux/kvm_host.h>
+#include <linux/pseudo_fs.h>
#include <linux/pagemap.h>
#include <linux/anon_inodes.h>
#include "kvm_mm.h"
+static struct vfsmount *kvm_gmem_mnt;
+
struct kvm_gmem {
struct kvm *kvm;
struct xarray bindings;
@@ -307,6 +312,38 @@ static pgoff_t kvm_gmem_get_index(struct kvm_memory_slot *slot, gfn_t gfn)
return gfn - slot->base_gfn + slot->gmem.pgoff;
}
+static const struct super_operations kvm_gmem_super_operations = {
+ .statfs = simple_statfs,
+};
+
+static int kvm_gmem_init_fs_context(struct fs_context *fc)
+{
+ struct pseudo_fs_context *ctx;
+
+ if (!init_pseudo(fc, GUEST_MEMORY_MAGIC))
+ return -ENOMEM;
+
+ ctx = fc->fs_private;
+ ctx->ops = &kvm_gmem_super_operations;
+
+ return 0;
+}
+
+static struct file_system_type kvm_gmem_fs = {
+ .name = "kvm_guest_memory",
+ .init_fs_context = kvm_gmem_init_fs_context,
+ .kill_sb = kill_anon_super,
+};
+
+static void kvm_gmem_init_mount(void)
+{
+ kvm_gmem_mnt = kern_mount(&kvm_gmem_fs);
+ BUG_ON(IS_ERR(kvm_gmem_mnt));
+
+ /* For giggles. Userspace can never map this anyways. */
+ kvm_gmem_mnt->mnt_flags |= MNT_NOEXEC;
+}
+
static struct file_operations kvm_gmem_fops = {
.open = generic_file_open,
.release = kvm_gmem_release,
@@ -316,6 +353,8 @@ static struct file_operations kvm_gmem_fops = {
void kvm_gmem_init(struct module *module)
{
kvm_gmem_fops.owner = module;
+
+ kvm_gmem_init_mount();
}
static int kvm_gmem_migrate_folio(struct address_space *mapping,
@@ -397,11 +436,67 @@ static const struct inode_operations kvm_gmem_iops = {
.setattr = kvm_gmem_setattr,
};
+static struct inode *kvm_gmem_inode_make_secure_inode(const char *name,
+ loff_t size, u64 flags)
+{
+ const struct qstr qname = QSTR_INIT(name, strlen(name));
+ struct inode *inode;
+ int err;
+
+ inode = alloc_anon_inode(kvm_gmem_mnt->mnt_sb);
+ if (IS_ERR(inode))
+ return inode;
+
+ err = security_inode_init_security_anon(inode, &qname, NULL);
+ if (err) {
+ iput(inode);
+ return ERR_PTR(err);
+ }
+
+ 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;
+ inode->i_size = size;
+ mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER);
+ mapping_set_inaccessible(inode->i_mapping);
+ /* Unmovable mappings are supposed to be marked unevictable as well. */
+ WARN_ON_ONCE(!mapping_unevictable(inode->i_mapping));
+
+ return inode;
+}
+
+static struct file *kvm_gmem_inode_create_getfile(void *priv, loff_t size,
+ u64 flags)
+{
+ static const char *name = "[kvm-gmem]";
+ struct inode *inode;
+ struct file *file;
+
+ if (kvm_gmem_fops.owner && !try_module_get(kvm_gmem_fops.owner))
+ return ERR_PTR(-ENOENT);
+
The validation on 'kvm_gmem_fops.owner' can be removed since try_module_get()
and module_put() are friendly to a NULL parameter, even when CONFIG_MODULE_UNLOAD == N
A module_put(kvm_gmem_fops.owner) is needed in the various erroneous cases in
this function. Otherwise, the reference count of the owner (module) will become
imbalanced on any errors.
+ inode = kvm_gmem_inode_make_secure_inode(name, size, flags);
+ if (IS_ERR(inode))
+ return ERR_CAST(inode);
+
ERR_CAST may be dropped since there is nothing to be casted or converted?
+ file = alloc_file_pseudo(inode, kvm_gmem_mnt, name, O_RDWR,
+ &kvm_gmem_fops);
+ if (IS_ERR(file)) {
+ iput(inode);
+ return file;
+ }
+
+ file->f_mapping = inode->i_mapping;
+ file->f_flags |= O_LARGEFILE;
+ file->private_data = priv;
+
'file->f_mapping = inode->i_mapping' may be dropped since it's already correctly
set by alloc_file_pseudo().
alloc_file_pseudo
alloc_path_pseudo
alloc_file
alloc_empty_file
file_init_path // Set by this function
+ return file;
+}
+
static int __kvm_gmem_create(struct kvm *kvm, loff_t size, u64 flags)
{
- const char *anon_name = "[kvm-gmem]";
struct kvm_gmem *gmem;
- struct inode *inode;
struct file *file;
int fd, err;
@@ -415,32 +510,16 @@ static int __kvm_gmem_create(struct kvm *kvm, loff_t size, u64 flags)
goto err_fd;
}
- file = anon_inode_create_getfile(anon_name, &kvm_gmem_fops, gmem,
- O_RDWR, NULL);
+ file = kvm_gmem_inode_create_getfile(gmem, size, flags);
if (IS_ERR(file)) {
err = PTR_ERR(file);
goto err_gmem;
}
- file->f_flags |= O_LARGEFILE;
-
- inode = file->f_inode;
- WARN_ON(file->f_mapping != inode->i_mapping);
-
- 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;
- inode->i_size = size;
- mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER);
- mapping_set_inaccessible(inode->i_mapping);
- /* Unmovable mappings are supposed to be marked unevictable as well. */
- WARN_ON_ONCE(!mapping_unevictable(inode->i_mapping));
-
kvm_get_kvm(kvm);
gmem->kvm = kvm;
xa_init(&gmem->bindings);
- list_add(&gmem->entry, &inode->i_mapping->i_private_list);
+ list_add(&gmem->entry, &file_inode(file)->i_mapping->i_private_list);
fd_install(fd, file);
return fd;
Thanks,
Gavin
