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

[David Matlack <dmatlack@google.com>]

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;
+
 	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.
+ * 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
+ *
+ * VFIO uses the ABI defined below for preserving 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 */
-- 
2.53.0.983.g0bb29b3bc5-goog