Re: [PATCH v2 04/22] vfio/pci: Register a file handler with Live Update Orchestrator

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

On 1/29/26 1:24 PM, 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.
>
> 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/Makefile              |  1 +
>   drivers/vfio/pci/vfio_pci.c            |  9 +++-
>   drivers/vfio/pci/vfio_pci_liveupdate.c | 69 ++++++++++++++++++++++++++
>   drivers/vfio/pci/vfio_pci_priv.h       | 14 ++++++
>   include/linux/kho/abi/vfio_pci.h       | 28 +++++++++++
>   6 files changed, 121 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 a671e3d4e8be..7d6cdecedb05 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -27520,6 +27520,7 @@ 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/Makefile b/drivers/vfio/pci/Makefile
> index e0a0757dd1d2..23305ebc418b 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-$(CONFIG_LIVEUPDATE) += vfio_pci_liveupdate.o
>   obj-$(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..19e88322af2c 100644
> --- a/drivers/vfio/pci/vfio_pci.c
> +++ b/drivers/vfio/pci/vfio_pci.c
> @@ -258,6 +258,10 @@ static int __init vfio_pci_init(void)
>   	int ret;
>   	bool is_disable_vga = true;
>   
> +	ret = vfio_pci_liveupdate_init();
> +	if (ret)
> +		return ret;
> +
>   #ifdef CONFIG_VFIO_PCI_VGA
>   	is_disable_vga = disable_vga;
>   #endif
> @@ -266,8 +270,10 @@ static int __init vfio_pci_init(void)
>   
>   	/* Register and scan for devices */
>   	ret = pci_register_driver(&vfio_pci_driver);
> -	if (ret)
> +	if (ret) {
> +		vfio_pci_liveupdate_cleanup();
>   		return ret;
> +	}
>   
>   	vfio_pci_fill_ids();
>   
> @@ -281,6 +287,7 @@ 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..b84e63c0357b
> --- /dev/null
> +++ b/drivers/vfio/pci/vfio_pci_liveupdate.c
> @@ -0,0 +1,69 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +/*
> + * Copyright (c) 2025, 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)
> +{
> +	if (!liveupdate_enabled())
> +		return 0;
813 int liveupdate_register_file_handler(struct liveupdate_file_handler *fh)
814 {
815         struct liveupdate_file_handler *fh_iter;
816         int err;
817
818         if (!liveupdate_enabled())

819                 return -EOPNOTSUPP;

In the function liveupdate_register_file_handler, liveupdate_enabled is also checked.
as such, it is not necessary to check here?

+
+	return liveupdate_register_file_handler(&vfio_pci_liveupdate_fh);
+}
+
+void vfio_pci_liveupdate_cleanup(void)
+{
+	if (!liveupdate_enabled())
+		return;
+


ditto

Zhu Yanjun

> +	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..68966ec64e51 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_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_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..37a845eed972
> --- /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.
> + * Vipin Sharma <vipinsh@google.com>
> + * David Matlack <dmatlack@google.com>
> + */
> +
> +#ifndef _LINUX_LIVEUPDATE_ABI_VFIO_PCI_H
> +#define _LINUX_LIVEUPDATE_ABI_VFIO_PCI_H
> +
> +/**
> + * DOC: VFIO PCI Live Update ABI
> + *
> + * This header defines the ABI for preserving the state of a VFIO PCI device
> + * files across a kexec reboot using LUO.
> + *
> + * Device metadata is serialized into memory which is then handed to the next
> + * kernel via KHO.
> + *
> + * This interface is a contract. Any modification to any of the serialization
> + * structs defined here constitutes a breaking change. Such changes require
> + * incrementing the version number in the VFIO_PCI_LUO_FH_COMPATIBLE string.
> + */
> +
> +#define VFIO_PCI_LUO_FH_COMPATIBLE "vfio-pci-v1"
> +
> +#endif /* _LINUX_LIVEUPDATE_ABI_VFIO_PCI_H */