[PATCH v2 08/22] vfio: Enforce preserved devices are retrieved via LIVEUPDATE_SESSION_RETRIEVE_FD

David Matlack
2026-01-29T21:25:51Z

Enforce that files for incoming (preserved by previous kernel) VFIO
devices are retrieved via LIVEUPDATE_SESSION_RETRIEVE_FD rather than by
opening the corresponding VFIO character device or via
VFIO_GROUP_GET_DEVICE_FD.

Both of these methods would result in VFIO initializing the device
without access to the preserved state of the device passed by the
previous kernel.

Signed-off-by: David Matlack <dmatlack@google.com>
---
drivers/vfio/device_cdev.c | 4 ++++
drivers/vfio/group.c | 9 +++++++++
include/linux/vfio.h | 18 ++++++++++++++++++
3 files changed, 31 insertions(+)

diff --git a/drivers/vfio/device_cdev.c b/drivers/vfio/device_cdev.c
index 935f84a35875..355447e2add3 100644
--- a/drivers/vfio/device_cdev.c
+++ b/drivers/vfio/device_cdev.c
@@ -57,6 +57,10 @@ int vfio_device_fops_cdev_open(struct inode *inode, struct file *filep)
struct vfio_device *device = container_of(inode->i_cdev,
struct vfio_device, cdev);

+ /* Device file must be retrieved via LIVEUPDATE_SESSION_RETRIEVE_FD */
+ if (vfio_liveupdate_incoming_is_preserved(device))
+ return -EBUSY;
+
return __vfio_device_fops_cdev_open(device, filep);
}

diff --git a/drivers/vfio/group.c b/drivers/vfio/group.c
index d47ffada6912..63fc4d656215 100644
--- a/drivers/vfio/group.c
+++ b/drivers/vfio/group.c
@@ -311,6 +311,15 @@ static int vfio_group_ioctl_get_device_fd(struct vfio_group *group,
if (IS_ERR(device))
return PTR_ERR(device);

+ /*
+ * This device was preserved across a Live Update. Accessing it via
+ * VFIO_GROUP_GET_DEVICE_FD is not allowed.
+ */
+ if (vfio_liveupdate_incoming_is_preserved(device)) {
+ vfio_device_put_registration(device);
+ return -EBUSY;
+ }
+
fd = FD_ADD(O_CLOEXEC, vfio_device_open_file(device));
if (fd < 0)
vfio_device_put_registration(device);
diff --git a/include/linux/vfio.h b/include/linux/vfio.h
index dc592dc00f89..0921847b18b5 100644
--- a/include/linux/vfio.h
+++ b/include/linux/vfio.h
@@ -16,6 +16,7 @@
#include <linux/cdev.h>
#include <uapi/linux/vfio.h>
#include <linux/iova_bitmap.h>
+#include <linux/pci.h>

struct kvm;
struct iommufd_ctx;
@@ -431,4 +432,21 @@ static inline int __vfio_device_fops_cdev_open(struct vfio_device *device,

struct vfio_device *vfio_find_device(const void *data, device_match_t match);

+#ifdef CONFIG_LIVEUPDATE
+static inline bool vfio_liveupdate_incoming_is_preserved(struct vfio_device *device)
+{
+ struct device *d = device->dev;
+
+ if (dev_is_pci(d))
+ return to_pci_dev(d)->liveupdate_incoming;
+
+ return false;
+}
+#else
+static inline bool vfio_liveupdate_incoming_is_preserved(struct vfio_device *device)
+{
+ return false;
+}
+#endif
+
#endif /* VFIO_H */
--
2.53.0.rc1.225.gd81095ad13-goog