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Message-ID: <754b4898c3362050071f6dd09deb24f3c92a41c3.1747368092.git.afranji@google.com>
Date: Fri, 16 May 2025 19:19:22 +0000
From: Ryan Afranji <afranji@...gle.com>
To: afranji@...gle.com, ackerleytng@...gle.com, pbonzini@...hat.com,
seanjc@...gle.com, tglx@...utronix.de, x86@...nel.org, kvm@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
tabba@...gle.com
Cc: mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com, hpa@...or.com,
shuah@...nel.org, andrew.jones@...ux.dev, ricarkol@...gle.com,
chao.p.peng@...ux.intel.com, jarkko@...nel.org, yu.c.zhang@...ux.intel.com,
vannapurve@...gle.com, erdemaktas@...gle.com, mail@...iej.szmigiero.name,
vbabka@...e.cz, david@...hat.com, qperret@...gle.com, michael.roth@....com,
wei.w.wang@...el.com, liam.merwick@...cle.com, isaku.yamahata@...il.com,
kirill.shutemov@...ux.intel.com, sagis@...gle.com, jthoughton@...gle.com
Subject: [RFC PATCH v2 02/13] 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: Fuad Tabba <tabba@...gle.com>
Signed-off-by: Ackerley Tng <ackerleytng@...gle.com>
---
include/uapi/linux/magic.h | 1 +
virt/kvm/guest_memfd.c | 132 +++++++++++++++++++++++++++++++------
virt/kvm/kvm_main.c | 7 +-
virt/kvm/kvm_mm.h | 9 ++-
4 files changed, 124 insertions(+), 25 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 b2aa6bf24d3a..2ee26695dc31 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -1,12 +1,16 @@
// SPDX-License-Identifier: GPL-2.0
+#include <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;
@@ -318,9 +322,51 @@ static struct file_operations kvm_gmem_fops = {
.fallocate = kvm_gmem_fallocate,
};
-void kvm_gmem_init(struct module *module)
+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 int kvm_gmem_init_mount(void)
+{
+ kvm_gmem_mnt = kern_mount(&kvm_gmem_fs);
+
+ if (WARN_ON_ONCE(IS_ERR(kvm_gmem_mnt)))
+ return PTR_ERR(kvm_gmem_mnt);
+
+ kvm_gmem_mnt->mnt_flags |= MNT_NOEXEC;
+ return 0;
+}
+
+int kvm_gmem_init(struct module *module)
{
kvm_gmem_fops.owner = module;
+
+ return kvm_gmem_init_mount();
+}
+
+void kvm_gmem_exit(void)
+{
+ kern_unmount(kvm_gmem_mnt);
+ kvm_gmem_mnt = NULL;
}
static int kvm_gmem_migrate_folio(struct address_space *mapping,
@@ -402,11 +448,71 @@ 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)
+{
+ struct inode *inode;
+
+ inode = alloc_anon_secure_inode(kvm_gmem_mnt->mnt_sb, name);
+ if (IS_ERR(inode))
+ return inode;
+
+ 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;
@@ -420,32 +526,16 @@ 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;
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 69782df3617f..1e3fd81868bc 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -6412,7 +6412,9 @@ int kvm_init(unsigned vcpu_size, unsigned vcpu_align, struct module *module)
if (WARN_ON_ONCE(r))
goto err_vfio;
- kvm_gmem_init(module);
+ r = kvm_gmem_init(module);
+ if (r)
+ goto err_gmem;
r = kvm_init_virtualization();
if (r)
@@ -6433,6 +6435,8 @@ int kvm_init(unsigned vcpu_size, unsigned vcpu_align, struct module *module)
err_register:
kvm_uninit_virtualization();
err_virt:
+ kvm_gmem_exit();
+err_gmem:
kvm_vfio_ops_exit();
err_vfio:
kvm_async_pf_deinit();
@@ -6464,6 +6468,7 @@ void kvm_exit(void)
for_each_possible_cpu(cpu)
free_cpumask_var(per_cpu(cpu_kick_mask, cpu));
kmem_cache_destroy(kvm_vcpu_cache);
+ kvm_gmem_exit();
kvm_vfio_ops_exit();
kvm_async_pf_deinit();
kvm_irqfd_exit();
diff --git a/virt/kvm/kvm_mm.h b/virt/kvm/kvm_mm.h
index acef3f5c582a..dcacb76b8f00 100644
--- a/virt/kvm/kvm_mm.h
+++ b/virt/kvm/kvm_mm.h
@@ -68,17 +68,20 @@ static inline void gfn_to_pfn_cache_invalidate_start(struct kvm *kvm,
#endif /* HAVE_KVM_PFNCACHE */
#ifdef CONFIG_KVM_PRIVATE_MEM
-void kvm_gmem_init(struct module *module);
+int kvm_gmem_init(struct module *module);
+void kvm_gmem_exit(void);
int kvm_gmem_create(struct kvm *kvm, struct kvm_create_guest_memfd *args);
int kvm_gmem_bind(struct kvm *kvm, struct kvm_memory_slot *slot,
unsigned int fd, loff_t offset);
void kvm_gmem_unbind(struct kvm_memory_slot *slot);
#else
-static inline void kvm_gmem_init(struct module *module)
+static inline int kvm_gmem_init(struct module *module)
{
-
+ return 0;
}
+static inline void kvm_gmem_exit(void) {};
+
static inline int kvm_gmem_bind(struct kvm *kvm,
struct kvm_memory_slot *slot,
unsigned int fd, loff_t offset)
--
2.49.0.1101.gccaa498523-goog
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