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Message-ID: <20250408112402.181574-6-shivankg@amd.com>
Date: Tue, 8 Apr 2025 11:23:59 +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 5/8] KVM: guest_memfd: Make guest mem use guest mem inodes instead of anonymous inodes
From: Ackerley Tng <ackerleytng@...gle.com>
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@...gle.com>
Signed-off-by: Fuad Tabba <tabba@...gle.com>
Signed-off-by: Shivank Garg <shivankg@....com>
---
include/uapi/linux/magic.h | 1 +
virt/kvm/guest_memfd.c | 133 +++++++++++++++++++++++++++++++------
2 files changed, 113 insertions(+), 21 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 88453b040926..002328569c9e 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>
#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;
@@ -312,6 +317,38 @@ 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,
@@ -321,11 +358,13 @@ static struct file_operations kvm_gmem_fops = {
void kvm_gmem_init(struct module *module)
{
kvm_gmem_fops.owner = module;
+
+ kvm_gmem_init_mount();
}
void kvm_gmem_exit(void)
{
-
+ kern_unmount(kvm_gmem_mnt);
}
static int kvm_gmem_migrate_folio(struct address_space *mapping,
@@ -407,11 +446,79 @@ 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;
+ int err;
+
+ err = -ENOENT;
+ if (!try_module_get(kvm_gmem_fops.owner))
+ goto err;
+
+ inode = kvm_gmem_inode_make_secure_inode(name, size, flags);
+ if (IS_ERR(inode)) {
+ err = PTR_ERR(inode);
+ goto err_put_module;
+ }
+
+ file = alloc_file_pseudo(inode, kvm_gmem_mnt, name, O_RDWR,
+ &kvm_gmem_fops);
+ if (IS_ERR(file)) {
+ err = PTR_ERR(file);
+ goto err_put_inode;
+ }
+
+ file->f_flags |= O_LARGEFILE;
+ file->private_data = priv;
+
+out:
+ return file;
+
+err_put_inode:
+ iput(inode);
+err_put_module:
+ module_put(kvm_gmem_fops.owner);
+err:
+ file = ERR_PTR(err);
+ goto out;
+}
+
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;
@@ -425,32 +532,16 @@ 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;
--
2.34.1
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