[PATCH v2 06/22] vfio/pci: Retrieve preserved device files after Live Update
Alex Williamson
alex at shazbot.org
Thu Feb 26 14:52:22 PST 2026
On Thu, 29 Jan 2026 21:24:53 +0000
David Matlack <dmatlack at google.com> wrote:
> From: Vipin Sharma <vipinsh at 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 at google.com>
> Co-developed-by: David Matlack <dmatlack at google.com>
> Signed-off-by: David Matlack <dmatlack at 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(-)
>
> 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);
I really dislike that we're exporting the underscore variant, which
implies it's an internal function that the caller should understand the
constraints, without outlining any constraints.
I'm not sure what a good alternative is. We can drop fops since this
isn't called from file_operations. Maybe vfio_device_cdev_open_file().
> +
> +/*
> + * 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);
Don't we end up calling vfio_device_fops.release with NULL
file->private_data here with inevitable segfaults? Thanks,
Alex
> + 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 */
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