Re: [PATCH v4 05/16] vfio: Enforce preserved devices are retrieved via LIVEUPDATE_SESSION_RETRIEVE_FD

[Zhu Yanjun <yanjun.zhu@linux.dev>]

在 2026/5/11 16:47, Vipin Sharma 写道:
> From: David Matlack <dmatlack@google.com>
>
> 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.
>
> Reviewed-by: Pranjal Shrivastava <praan@google.com>
> Signed-off-by: David Matlack <dmatlack@google.com>
> Co-developed-by: Vipin Sharma <vipinsh@google.com>
> Signed-off-by: Vipin Sharma <vipinsh@google.com>
> ---
>   drivers/vfio/device_cdev.c             |  8 ++++++++
>   drivers/vfio/group.c                   |  9 +++++++++
>   drivers/vfio/pci/vfio_pci_liveupdate.c |  6 ++++++
>   drivers/vfio/vfio.h                    | 18 ++++++++++++++++++
>   4 files changed, 41 insertions(+)
>
> diff --git a/drivers/vfio/device_cdev.c b/drivers/vfio/device_cdev.c
> index 1ab07ccaf3ab..4df0495941c6 100644
> --- a/drivers/vfio/device_cdev.c
> +++ b/drivers/vfio/device_cdev.c
> @@ -49,6 +49,14 @@ static int vfio_device_cdev_open(struct vfio_device *device, struct file **filep
>   		}
>   
>   		*filep = file;
> +	} else if (vfio_liveupdate_incoming_is_preserved(device)) {
> +		/*
> +		 * Since it is live update preserved device, it must be
> +		 * retrieved via LIVEUPDATE_SESSION_RETRIEVE_FD instead of
> +		 * opening /dev/vfio/devices/vfioX.
> +		 */
> +		ret = -EBUSY;
> +		goto err_free_device_file;

When vfio_liveupdate_incoming_is_preserved(device) returns true, 
vfio_device_put_registration(device) is not called in this path.

Is vfio_device_put_registration(device) instead invoked from the 
err_free_device_file error handling path?

Zhu Yanjun

>   	}
>   
>   	file->private_data = df;
> diff --git a/drivers/vfio/group.c b/drivers/vfio/group.c
> index b2299e5bc6df..62b4eaabc829 100644
> --- a/drivers/vfio/group.c
> +++ b/drivers/vfio/group.c
> @@ -316,6 +316,15 @@ 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/drivers/vfio/pci/vfio_pci_liveupdate.c b/drivers/vfio/pci/vfio_pci_liveupdate.c
> index 11c3bc8a8dcd..731a3e34085f 100644
> --- a/drivers/vfio/pci/vfio_pci_liveupdate.c
> +++ b/drivers/vfio/pci/vfio_pci_liveupdate.c
> @@ -47,6 +47,12 @@
>    *   ...
>    *   ioctl(session_fd, LIVEUPDATE_SESSION_FINISH, ...);
>    *
> + * .. note::
> + *    After kexec, if a device was preserved by the previous kernel, attempting
> + *    to open a new file for the device via its character device
> + *    (``/dev/vfio/devices/X``) or via ``VFIO_GROUP_GET_DEVICE_FD`` will fail
> + *    with ``-EBUSY``.
> + *
>    * Restrictions
>    * ============
>    *
> diff --git a/drivers/vfio/vfio.h b/drivers/vfio/vfio.h
> index 0854f3fa1a22..5269fe021ee3 100644
> --- a/drivers/vfio/vfio.h
> +++ b/drivers/vfio/vfio.h
> @@ -11,6 +11,7 @@
>   #include <linux/cdev.h>
>   #include <linux/module.h>
>   #include <linux/vfio.h>
> +#include <linux/pci.h>
>   
>   struct iommufd_ctx;
>   struct iommu_group;
> @@ -461,4 +462,21 @@ static inline void vfio_device_debugfs_init(struct vfio_device *vdev) { }
>   static inline void vfio_device_debugfs_exit(struct vfio_device *vdev) { }
>   #endif /* CONFIG_VFIO_DEBUGFS */
>   
> +#ifdef CONFIG_PCI_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 /* CONFIG_PCI_LIVEUPDATE */
> +
>   #endif

-- 
Best Regards,
Yanjun.Zhu