Re: [PATCH v3 06/24] vfio/pci: Register a file handler with Live Update Orchestrator

[Yi Liu <yi.l.liu@intel.com>]

On 3/24/26 07:57, David Matlack wrote:
> From: Vipin Sharma <vipinsh@google.com>
> 
> Register a live update file handler for vfio-pci device files. Add stub
> implementations of all required callbacks so that registration does not
> fail (i.e. to avoid breaking git-bisect).
> 
> This file handler will be extended in subsequent commits to enable a
> device bound to vfio-pci to run without interruption while the host is
> going through a kexec Live Update.
> 
> Put this support behind a new Kconfig VFIO_PCI_LIVEUPDATE that is marked
> experimental and default-disabled until more of the device preservation
> support has landed in the kernel.
> 
> Signed-off-by: Vipin Sharma <vipinsh@google.com>
> Co-developed-by: David Matlack <dmatlack@google.com>
> Signed-off-by: David Matlack <dmatlack@google.com>
> ---
>   MAINTAINERS                            |  1 +
>   drivers/vfio/pci/Kconfig               | 11 ++++
>   drivers/vfio/pci/Makefile              |  1 +
>   drivers/vfio/pci/vfio_pci.c            | 12 ++++-
>   drivers/vfio/pci/vfio_pci_liveupdate.c | 69 ++++++++++++++++++++++++++
>   drivers/vfio/pci/vfio_pci_priv.h       | 14 ++++++
>   include/linux/kho/abi/vfio_pci.h       | 28 +++++++++++
>   7 files changed, 135 insertions(+), 1 deletion(-)
>   create mode 100644 drivers/vfio/pci/vfio_pci_liveupdate.c
>   create mode 100644 include/linux/kho/abi/vfio_pci.h
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 96ea84948d76..a16a7ecc67a4 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -27685,6 +27685,7 @@ F:	Documentation/ABI/testing/debugfs-vfio
>   F:	Documentation/ABI/testing/sysfs-devices-vfio-dev
>   F:	Documentation/driver-api/vfio.rst
>   F:	drivers/vfio/
> +F:	include/linux/kho/abi/vfio_pci.h
>   F:	include/linux/vfio.h
>   F:	include/linux/vfio_pci_core.h
>   F:	include/uapi/linux/vfio.h
> diff --git a/drivers/vfio/pci/Kconfig b/drivers/vfio/pci/Kconfig
> index 1e82b44bda1a..8f087f7b58c3 100644
> --- a/drivers/vfio/pci/Kconfig
> +++ b/drivers/vfio/pci/Kconfig
> @@ -58,6 +58,17 @@ config VFIO_PCI_ZDEV_KVM
>   config VFIO_PCI_DMABUF
>   	def_bool y if VFIO_PCI_CORE && PCI_P2PDMA && DMA_SHARED_BUFFER
>   
> +config VFIO_PCI_LIVEUPDATE
> +	bool "VFIO PCI support for Live Update (EXPERIMENTAL)"
> +	depends on VFIO_PCI && PCI_LIVEUPDATE
> +	help
> +	  Support for preserving devices bound to vfio-pci across a Live
> +	  Update. This option should only be enabled by developers working on
> +	  implementing this support. Once enough support has landed in the
> +	  kernel, this option will no longer be marked EXPERIMENTAL.
> +
> +	  If you don't know what to do here, say N.
> +
>   source "drivers/vfio/pci/mlx5/Kconfig"
>   
>   source "drivers/vfio/pci/hisilicon/Kconfig"
> diff --git a/drivers/vfio/pci/Makefile b/drivers/vfio/pci/Makefile
> index e0a0757dd1d2..f462df61edb9 100644
> --- a/drivers/vfio/pci/Makefile
> +++ b/drivers/vfio/pci/Makefile
> @@ -7,6 +7,7 @@ obj-$(CONFIG_VFIO_PCI_CORE) += vfio-pci-core.o
>   
>   vfio-pci-y := vfio_pci.o
>   vfio-pci-$(CONFIG_VFIO_PCI_IGD) += vfio_pci_igd.o
> +vfio-pci-$(CONFIG_VFIO_PCI_LIVEUPDATE) += vfio_pci_liveupdate.o
>   obj-$(CONFIG_VFIO_PCI) += vfio-pci.o
>   
>   obj-$(CONFIG_MLX5_VFIO_PCI)           += mlx5/
> diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> index 0c771064c0b8..41dcbe4ace67 100644
> --- a/drivers/vfio/pci/vfio_pci.c
> +++ b/drivers/vfio/pci/vfio_pci.c
> @@ -170,6 +170,7 @@ static int vfio_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
>   	ret = vfio_pci_core_register_device(vdev);
>   	if (ret)
>   		goto out_put_vdev;
> +

a meaningless line here.

>   	return 0;
>   
>   out_put_vdev:
> @@ -264,10 +265,14 @@ static int __init vfio_pci_init(void)
>   
>   	vfio_pci_core_set_params(nointxmask, is_disable_vga, disable_idle_d3);
>   
> +	ret = vfio_pci_liveupdate_init();
> +	if (ret)
> +		return ret;
> +
>   	/* Register and scan for devices */
>   	ret = pci_register_driver(&vfio_pci_driver);
>   	if (ret)
> -		return ret;
> +		goto err_liveupdate_cleanup;
>   
>   	vfio_pci_fill_ids();
>   
> @@ -275,12 +280,17 @@ static int __init vfio_pci_init(void)
>   		pr_warn("device denylist disabled.\n");
>   
>   	return 0;
> +
> +err_liveupdate_cleanup:
> +	vfio_pci_liveupdate_cleanup();
> +	return ret;
>   }
>   module_init(vfio_pci_init);
>   
>   static void __exit vfio_pci_cleanup(void)
>   {
>   	pci_unregister_driver(&vfio_pci_driver);
> +	vfio_pci_liveupdate_cleanup();
>   }
>   module_exit(vfio_pci_cleanup);
>   
> diff --git a/drivers/vfio/pci/vfio_pci_liveupdate.c b/drivers/vfio/pci/vfio_pci_liveupdate.c
> new file mode 100644
> index 000000000000..5ea5af46b159
> --- /dev/null
> +++ b/drivers/vfio/pci/vfio_pci_liveupdate.c
> @@ -0,0 +1,69 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +/*
> + * Copyright (c) 2026, Google LLC.
> + * Vipin Sharma <vipinsh@google.com>
> + * David Matlack <dmatlack@google.com>
> + */
> +
> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> +
> +#include <linux/kho/abi/vfio_pci.h>
> +#include <linux/liveupdate.h>
> +#include <linux/errno.h>
> +
> +#include "vfio_pci_priv.h"
> +
> +static bool vfio_pci_liveupdate_can_preserve(struct liveupdate_file_handler *handler,
> +					     struct file *file)
> +{
> +	return false;
> +}
> +
> +static int vfio_pci_liveupdate_preserve(struct liveupdate_file_op_args *args)
> +{
> +	return -EOPNOTSUPP;
> +}
> +
> +static void vfio_pci_liveupdate_unpreserve(struct liveupdate_file_op_args *args)
> +{
> +}
> +
> +static int vfio_pci_liveupdate_retrieve(struct liveupdate_file_op_args *args)
> +{
> +	return -EOPNOTSUPP;
> +}
> +
> +static void vfio_pci_liveupdate_finish(struct liveupdate_file_op_args *args)
> +{
> +}
> +
> +static const struct liveupdate_file_ops vfio_pci_liveupdate_file_ops = {
> +	.can_preserve = vfio_pci_liveupdate_can_preserve,
> +	.preserve = vfio_pci_liveupdate_preserve,
> +	.unpreserve = vfio_pci_liveupdate_unpreserve,
> +	.retrieve = vfio_pci_liveupdate_retrieve,
> +	.finish = vfio_pci_liveupdate_finish,
> +	.owner = THIS_MODULE,
> +};
> +
> +static struct liveupdate_file_handler vfio_pci_liveupdate_fh = {
> +	.ops = &vfio_pci_liveupdate_file_ops,
> +	.compatible = VFIO_PCI_LUO_FH_COMPATIBLE,
> +};
> +
> +int __init vfio_pci_liveupdate_init(void)
> +{
> +	int ret;
> +
> +	ret = liveupdate_register_file_handler(&vfio_pci_liveupdate_fh);
> +	if (ret && ret != -EOPNOTSUPP)
> +		return ret;
> +
> +	return 0;
> +}
> +
> +void vfio_pci_liveupdate_cleanup(void)
> +{
> +       liveupdate_unregister_file_handler(&vfio_pci_liveupdate_fh);
> +}
> diff --git a/drivers/vfio/pci/vfio_pci_priv.h b/drivers/vfio/pci/vfio_pci_priv.h
> index 27ac280f00b9..cbf46e09da30 100644
> --- a/drivers/vfio/pci/vfio_pci_priv.h
> +++ b/drivers/vfio/pci/vfio_pci_priv.h
> @@ -133,4 +133,18 @@ static inline void vfio_pci_dma_buf_move(struct vfio_pci_core_device *vdev,
>   }
>   #endif
>   
> +#ifdef CONFIG_VFIO_PCI_LIVEUPDATE
> +int __init vfio_pci_liveupdate_init(void);
> +void vfio_pci_liveupdate_cleanup(void);
> +#else
> +static inline int vfio_pci_liveupdate_init(void)
> +{
> +	return 0;
> +}
> +
> +static inline void vfio_pci_liveupdate_cleanup(void)
> +{
> +}
> +#endif /* CONFIG_VFIO_PCI_LIVEUPDATE */
> +
>   #endif
> diff --git a/include/linux/kho/abi/vfio_pci.h b/include/linux/kho/abi/vfio_pci.h
> new file mode 100644
> index 000000000000..e2412b455e61
> --- /dev/null
> +++ b/include/linux/kho/abi/vfio_pci.h
> @@ -0,0 +1,28 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +/*
> + * Copyright (c) 2025, Google LLC.

would be nice to update 2025 to 2026 now. :)

Regards,
Yi Liu