Re: [PATCH v2 06/22] vfio/pci: Retrieve preserved device files after Live Update

[Pranjal Shrivastava <praan@google.com>]

On Thu, Jan 29, 2026 at 09:24:53PM +0000, David Matlack wrote:
> From: Vipin Sharma <vipinsh@google.com>
> 
> Enable userspace to retrieve preserved VFIO device files from VFIO after
> a Live Update by implementing the retrieve() and finish() file handler
> callbacks.
> 
> Use an anonymous inode when creating the file, since the retrieved
> device file is not opened through any particular cdev inode, and the
> cdev inode does not matter in practice.
> 
> For now the retrieved file is functionally equivalent a opening the
> corresponding VFIO cdev file. Subsequent commits will leverage the
> preserved state associated with the retrieved file to preserve bits of
> the device across Live Update.
> 
> Signed-off-by: Vipin Sharma <vipinsh@google.com>
> Co-developed-by: David Matlack <dmatlack@google.com>
> Signed-off-by: David Matlack <dmatlack@google.com>
> ---
>  drivers/vfio/device_cdev.c             | 21 ++++++---
>  drivers/vfio/pci/vfio_pci_liveupdate.c | 60 +++++++++++++++++++++++++-
>  drivers/vfio/vfio_main.c               | 13 ++++++
>  include/linux/vfio.h                   | 12 ++++++
>  4 files changed, 98 insertions(+), 8 deletions(-)
> 

The use of anon_inode_getfile_fmode() is clever! The abstraction is
clean as well. 

Reviewed-by: Pranjal Shrivastava <praan@google.com>

Thanks!
Praan

> diff --git a/drivers/vfio/device_cdev.c b/drivers/vfio/device_cdev.c
> index 8ceca24ac136..935f84a35875 100644
> --- a/drivers/vfio/device_cdev.c
> +++ b/drivers/vfio/device_cdev.c
> @@ -16,14 +16,8 @@ void vfio_init_device_cdev(struct vfio_device *device)
>  	device->cdev.owner = THIS_MODULE;
>  }
>  
> -/*
> - * device access via the fd opened by this function is blocked until
> - * .open_device() is called successfully during BIND_IOMMUFD.
> - */
> -int vfio_device_fops_cdev_open(struct inode *inode, struct file *filep)
> +int __vfio_device_fops_cdev_open(struct vfio_device *device, struct file *filep)
>  {
> -	struct vfio_device *device = container_of(inode->i_cdev,
> -						  struct vfio_device, cdev);
>  	struct vfio_device_file *df;
>  	int ret;
>  
> @@ -52,6 +46,19 @@ int vfio_device_fops_cdev_open(struct inode *inode, struct file *filep)
>  	vfio_device_put_registration(device);
>  	return ret;
>  }
> +EXPORT_SYMBOL_GPL(__vfio_device_fops_cdev_open);
> +
> +/*
> + * device access via the fd opened by this function is blocked until
> + * .open_device() is called successfully during BIND_IOMMUFD.
> + */
> +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);
> +
> +	return __vfio_device_fops_cdev_open(device, filep);
> +}
>  
>  static void vfio_df_get_kvm_safe(struct vfio_device_file *df)
>  {
> diff --git a/drivers/vfio/pci/vfio_pci_liveupdate.c b/drivers/vfio/pci/vfio_pci_liveupdate.c
> index f01de98f1b75..7f4117181fd0 100644
> --- a/drivers/vfio/pci/vfio_pci_liveupdate.c
> +++ b/drivers/vfio/pci/vfio_pci_liveupdate.c
> @@ -8,6 +8,8 @@
>  
>  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
>  
> +#include <linux/anon_inodes.h>
> +#include <linux/file.h>
>  #include <linux/kexec_handover.h>
>  #include <linux/kho/abi/vfio_pci.h>
>  #include <linux/liveupdate.h>
> @@ -108,13 +110,68 @@ static int vfio_pci_liveupdate_freeze(struct liveupdate_file_op_args *args)
>  	return ret;
>  }
>  
> +static int match_device(struct device *dev, const void *arg)
> +{
> +	struct vfio_device *device = container_of(dev, struct vfio_device, device);
> +	const struct vfio_pci_core_device_ser *ser = arg;
> +	struct pci_dev *pdev;
> +
> +	pdev = dev_is_pci(device->dev) ? to_pci_dev(device->dev) : NULL;
> +	if (!pdev)
> +		return false;
> +
> +	return ser->bdf == pci_dev_id(pdev) && ser->domain == pci_domain_nr(pdev->bus);
> +}
> +
>  static int vfio_pci_liveupdate_retrieve(struct liveupdate_file_op_args *args)
>  {
> -	return -EOPNOTSUPP;
> +	struct vfio_pci_core_device_ser *ser;
> +	struct vfio_device *device;
> +	struct file *file;
> +	int ret;
> +
> +	ser = phys_to_virt(args->serialized_data);
> +
> +	device = vfio_find_device(ser, match_device);
> +	if (!device)
> +		return -ENODEV;
> +
> +	/*
> +	 * Simulate opening the character device using an anonymous inode. The
> +	 * returned file has the same properties as a cdev file (e.g. operations
> +	 * are blocked until BIND_IOMMUFD is called).
> +	 */
> +	file = anon_inode_getfile_fmode("[vfio-device-liveupdate]",
> +					&vfio_device_fops, NULL,
> +					O_RDWR, FMODE_PREAD | FMODE_PWRITE);
> +	if (IS_ERR(file)) {
> +		ret = PTR_ERR(file);
> +		goto out;
> +	}
> +
> +	ret = __vfio_device_fops_cdev_open(device, file);
> +	if (ret) {
> +		fput(file);
> +		goto out;
> +	}
> +
> +	args->file = file;
> +
> +out:
> +	/* Drop the reference from vfio_find_device() */
> +	put_device(&device->device);
> +
> +	return ret;
> +}
> +
> +static bool vfio_pci_liveupdate_can_finish(struct liveupdate_file_op_args *args)
> +{
> +	return args->retrieved;
>  }
>  
>  static void vfio_pci_liveupdate_finish(struct liveupdate_file_op_args *args)
>  {
> +	kho_restore_free(phys_to_virt(args->serialized_data));
>  }
>  
>  static const struct liveupdate_file_ops vfio_pci_liveupdate_file_ops = {
> @@ -123,6 +180,7 @@ static const struct liveupdate_file_ops vfio_pci_liveupdate_file_ops = {
>  	.unpreserve = vfio_pci_liveupdate_unpreserve,
>  	.freeze = vfio_pci_liveupdate_freeze,
>  	.retrieve = vfio_pci_liveupdate_retrieve,
> +	.can_finish = vfio_pci_liveupdate_can_finish,
>  	.finish = vfio_pci_liveupdate_finish,
>  	.owner = THIS_MODULE,
>  };
> diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
> index 276f615f0c28..89c5feef75d5 100644
> --- a/drivers/vfio/vfio_main.c
> +++ b/drivers/vfio/vfio_main.c
> @@ -13,6 +13,7 @@
>  #include <linux/cdev.h>
>  #include <linux/compat.h>
>  #include <linux/device.h>
> +#include <linux/device/class.h>
>  #include <linux/fs.h>
>  #include <linux/idr.h>
>  #include <linux/iommu.h>
> @@ -1758,6 +1759,18 @@ int vfio_dma_rw(struct vfio_device *device, dma_addr_t iova, void *data,
>  }
>  EXPORT_SYMBOL(vfio_dma_rw);
>  
> +struct vfio_device *vfio_find_device(const void *data, device_match_t match)
> +{
> +	struct device *device;
> +
> +	device = class_find_device(vfio.device_class, NULL, data, match);
> +	if (!device)
> +		return NULL;
> +
> +	return container_of(device, struct vfio_device, device);
> +}
> +EXPORT_SYMBOL_GPL(vfio_find_device);
> +
>  /*
>   * Module/class support
>   */
> diff --git a/include/linux/vfio.h b/include/linux/vfio.h
> index 9aa1587fea19..dc592dc00f89 100644
> --- a/include/linux/vfio.h
> +++ b/include/linux/vfio.h
> @@ -419,4 +419,16 @@ int vfio_virqfd_enable(void *opaque, int (*handler)(void *, void *),
>  void vfio_virqfd_disable(struct virqfd **pvirqfd);
>  void vfio_virqfd_flush_thread(struct virqfd **pvirqfd);
>  
> +#if IS_ENABLED(CONFIG_VFIO_DEVICE_CDEV)
> +int __vfio_device_fops_cdev_open(struct vfio_device *device, struct file *filep);
> +#else
> +static inline int __vfio_device_fops_cdev_open(struct vfio_device *device,
> +					       struct file *filep)
> +{
> +	return -EOPNOTSUPP;
> +}
> +#endif /* IS_ENABLED(CONFIG_VFIO_DEVICE_CDEV) */
> +
> +struct vfio_device *vfio_find_device(const void *data, device_match_t match);
> +
>  #endif /* VFIO_H */
> -- 
> 2.53.0.rc1.225.gd81095ad13-goog
>