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X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 08 Apr 2025 11:25:20.1201 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: ed778027-b6c4-467a-edc8-08dd76900bcc X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[SATLEXMB04.amd.com] X-MS-Exchange-CrossTenant-AuthSource: SN1PEPF000397B2.namprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: SJ0PR12MB6968 Content-Type: text/plain; charset="utf-8" From: Ackerley Tng 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 Signed-off-by: Fuad Tabba Signed-off-by: Shivank Garg --- 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" */ =20 #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 +#include #include #include #include +#include #include #include =20 #include "kvm_mm.h" =20 +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_sl= ot *slot, gfn_t gfn) return gfn - slot->base_gfn + slot->gmem.pgoff; } =20 +static const struct super_operations kvm_gmem_super_operations =3D { + .statfs =3D 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 =3D fc->fs_private; + ctx->ops =3D &kvm_gmem_super_operations; + + return 0; +} + +static struct file_system_type kvm_gmem_fs =3D { + .name =3D "kvm_guest_memory", + .init_fs_context =3D kvm_gmem_init_fs_context, + .kill_sb =3D kill_anon_super, +}; + +static void kvm_gmem_init_mount(void) +{ + kvm_gmem_mnt =3D 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 |=3D MNT_NOEXEC; +} + static struct file_operations kvm_gmem_fops =3D { .open =3D generic_file_open, .release =3D kvm_gmem_release, @@ -321,11 +358,13 @@ static struct file_operations kvm_gmem_fops =3D { void kvm_gmem_init(struct module *module) { kvm_gmem_fops.owner =3D module; + + kvm_gmem_init_mount(); } =20 void kvm_gmem_exit(void) { - + kern_unmount(kvm_gmem_mnt); } =20 static int kvm_gmem_migrate_folio(struct address_space *mapping, @@ -407,11 +446,79 @@ static const struct inode_operations kvm_gmem_iops = =3D { .setattr =3D kvm_gmem_setattr, }; =20 +static struct inode *kvm_gmem_inode_make_secure_inode(const char *name, + loff_t size, u64 flags) +{ + const struct qstr qname =3D QSTR_INIT(name, strlen(name)); + struct inode *inode; + int err; + + inode =3D alloc_anon_inode(kvm_gmem_mnt->mnt_sb); + if (IS_ERR(inode)) + return inode; + + err =3D security_inode_init_security_anon(inode, &qname, NULL); + if (err) { + iput(inode); + return ERR_PTR(err); + } + + inode->i_private =3D (void *)(unsigned long)flags; + inode->i_op =3D &kvm_gmem_iops; + inode->i_mapping->a_ops =3D &kvm_gmem_aops; + inode->i_mode |=3D S_IFREG; + inode->i_size =3D 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 =3D "[kvm-gmem]"; + struct inode *inode; + struct file *file; + int err; + + err =3D -ENOENT; + if (!try_module_get(kvm_gmem_fops.owner)) + goto err; + + inode =3D kvm_gmem_inode_make_secure_inode(name, size, flags); + if (IS_ERR(inode)) { + err =3D PTR_ERR(inode); + goto err_put_module; + } + + file =3D alloc_file_pseudo(inode, kvm_gmem_mnt, name, O_RDWR, + &kvm_gmem_fops); + if (IS_ERR(file)) { + err =3D PTR_ERR(file); + goto err_put_inode; + } + + file->f_flags |=3D O_LARGEFILE; + file->private_data =3D priv; + +out: + return file; + +err_put_inode: + iput(inode); +err_put_module: + module_put(kvm_gmem_fops.owner); +err: + file =3D ERR_PTR(err); + goto out; +} + static int __kvm_gmem_create(struct kvm *kvm, loff_t size, u64 flags) { - const char *anon_name =3D "[kvm-gmem]"; struct kvm_gmem *gmem; - struct inode *inode; struct file *file; int fd, err; =20 @@ -425,32 +532,16 @@ static int __kvm_gmem_create(struct kvm *kvm, loff_t = size, u64 flags) goto err_fd; } =20 - file =3D anon_inode_create_getfile(anon_name, &kvm_gmem_fops, gmem, - O_RDWR, NULL); + file =3D kvm_gmem_inode_create_getfile(gmem, size, flags); if (IS_ERR(file)) { err =3D PTR_ERR(file); goto err_gmem; } =20 - file->f_flags |=3D O_LARGEFILE; - - inode =3D file->f_inode; - WARN_ON(file->f_mapping !=3D inode->i_mapping); - - inode->i_private =3D (void *)(unsigned long)flags; - inode->i_op =3D &kvm_gmem_iops; - inode->i_mapping->a_ops =3D &kvm_gmem_aops; - inode->i_mode |=3D S_IFREG; - inode->i_size =3D 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 =3D 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); =20 fd_install(fd, file); return fd; --=20 2.34.1