On Tue, Apr 08, 2025 at 11:23:59AM +0000, Shivank Garg wrote:
From: Ackerley Tng ackerleytng@google.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@google.com Signed-off-by: Fuad Tabba tabba@google.com Signed-off-by: Shivank Garg shivankg@amd.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);- }
So why do other alloc_anon_inode callers not need security_inode_init_security_anon?