Register VFIO live update file handler to Live Update Orchestrator.
Provide stub implementation of the handler callbacks.

Adding live update support in VFIO will enable a VFIO PCI device to work
uninterrupted while the host kernel is being updated through a kexec
reboot.

Signed-off-by: Vipin Sharma <vipinsh@google.com>
---
 drivers/vfio/pci/Makefile              |  1 +
 drivers/vfio/pci/vfio_pci_core.c       |  1 +
 drivers/vfio/pci/vfio_pci_liveupdate.c | 44 ++++++++++++++++++++++++++
 drivers/vfio/pci/vfio_pci_priv.h       |  6 ++++
 4 files changed, 52 insertions(+)
 create mode 100644 drivers/vfio/pci/vfio_pci_liveupdate.c

diff --git a/drivers/vfio/pci/Makefile b/drivers/vfio/pci/Makefile
index cf00c0a7e55c..929df22c079b 100644
--- a/drivers/vfio/pci/Makefile
+++ b/drivers/vfio/pci/Makefile
@@ -2,6 +2,7 @@
 
 vfio-pci-core-y := vfio_pci_core.o vfio_pci_intrs.o vfio_pci_rdwr.o vfio_pci_config.o
 vfio-pci-core-$(CONFIG_VFIO_PCI_ZDEV_KVM) += vfio_pci_zdev.o
+vfio-pci-core-$(CONFIG_LIVEUPDATE) += vfio_pci_liveupdate.o
 obj-$(CONFIG_VFIO_PCI_CORE) += vfio-pci-core.o
 
 vfio-pci-y := vfio_pci.o
diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
index 7dcf5439dedc..0894673a9262 100644
--- a/drivers/vfio/pci/vfio_pci_core.c
+++ b/drivers/vfio/pci/vfio_pci_core.c
@@ -2568,6 +2568,7 @@ static void vfio_pci_core_cleanup(void)
 static int __init vfio_pci_core_init(void)
 {
 	/* Allocate shared config space permission data used by all devices */
+	vfio_pci_liveupdate_init();
 	return vfio_pci_init_perm_bits();
 }
 
diff --git a/drivers/vfio/pci/vfio_pci_liveupdate.c b/drivers/vfio/pci/vfio_pci_liveupdate.c
new file mode 100644
index 000000000000..088f7698a72c
--- /dev/null
+++ b/drivers/vfio/pci/vfio_pci_liveupdate.c
@@ -0,0 +1,44 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Liveupdate support for VFIO devices.
+ *
+ * Copyright (c) 2025, Google LLC.
+ * Vipin Sharma <vipinsh@google.com>
+ */
+
+#include <linux/liveupdate.h>
+#include <linux/errno.h>
+
+#include "vfio_pci_priv.h"
+
+static int vfio_pci_liveupdate_retrieve(struct liveupdate_file_handler *handler,
+					u64 data, struct file **file)
+{
+	return -EOPNOTSUPP;
+}
+
+static bool vfio_pci_liveupdate_can_preserve(struct liveupdate_file_handler *handler,
+					     struct file *file)
+{
+	return -EOPNOTSUPP;
+}
+
+static const struct liveupdate_file_ops vfio_pci_luo_fops = {
+	.retrieve = vfio_pci_liveupdate_retrieve,
+	.can_preserve = vfio_pci_liveupdate_can_preserve,
+	.owner = THIS_MODULE,
+};
+
+static struct liveupdate_file_handler vfio_pci_luo_handler = {
+	.ops = &vfio_pci_luo_fops,
+	.compatible = "vfio-v1",
+};
+
+void __init vfio_pci_liveupdate_init(void)
+{
+	int err = liveupdate_register_file_handler(&vfio_pci_luo_handler);
+
+	if (err)
+		pr_err("VFIO PCI liveupdate file handler register failed, error %d.\n", err);
+}
diff --git a/drivers/vfio/pci/vfio_pci_priv.h b/drivers/vfio/pci/vfio_pci_priv.h
index a9972eacb293..7779fd744ff5 100644
--- a/drivers/vfio/pci/vfio_pci_priv.h
+++ b/drivers/vfio/pci/vfio_pci_priv.h
@@ -107,4 +107,10 @@ static inline bool vfio_pci_is_vga(struct pci_dev *pdev)
 	return (pdev->class >> 8) == PCI_CLASS_DISPLAY_VGA;
 }
 
+#ifdef CONFIG_LIVEUPDATE
+void vfio_pci_liveupdate_init(void);
+#else
+static inline void vfio_pci_liveupdate_init(void) { }
+#endif /* CONFIG_LIVEUPDATE */
+
 #endif
-- 
2.51.0.858.gf9c4a03a3a-goog

On Fri, Oct 17, 2025 at 5:07 PM Vipin Sharma <vipinsh@google.com> wrote:
> +static const struct liveupdate_file_ops vfio_pci_luo_fops = {
> +       .retrieve = vfio_pci_liveupdate_retrieve,
> +       .can_preserve = vfio_pci_liveupdate_can_preserve,
> +       .owner = THIS_MODULE,
> +};
> +
> +static struct liveupdate_file_handler vfio_pci_luo_handler = {
> +       .ops = &vfio_pci_luo_fops,
> +       .compatible = "vfio-v1",
> +};
> +
> +void __init vfio_pci_liveupdate_init(void)
> +{
> +       int err = liveupdate_register_file_handler(&vfio_pci_luo_handler);
> +
> +       if (err)
> +               pr_err("VFIO PCI liveupdate file handler register failed, error %d.\n", err);
> +}

Alex and Jason, should this go in the top-level VFIO directory? And
then have all the preservation logic go through vfio_device_ops? That
would make Live Update support for VFIO cdev files extensible to other
drivers in the future.

On Fri, Oct 17, 2025 at 5:07 PM Vipin Sharma <vipinsh@google.com> wrote:

> diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
>  static int __init vfio_pci_core_init(void)
>  {
>         /* Allocate shared config space permission data used by all devices */
> +       vfio_pci_liveupdate_init();
>         return vfio_pci_init_perm_bits();

The call to vfio_pci_liveupdate_init() should go before the comment
associated with vfio_pci_init_perm_bits().

> diff --git a/drivers/vfio/pci/vfio_pci_liveupdate.c b/drivers/vfio/pci/vfio_pci_liveupdate.c
> +static bool vfio_pci_liveupdate_can_preserve(struct liveupdate_file_handler *handler,
> +                                            struct file *file)
> +{
> +       return -EOPNOTSUPP;

can_preserve() returns a bool, so this should be "return false". But I
think we can just do the cdev fops check in this commit. It is a small
enough change.

> +static struct liveupdate_file_handler vfio_pci_luo_handler = {
> +       .ops = &vfio_pci_luo_fops,
> +       .compatible = "vfio-v1",

This should probably be something like "vfio-pci-v1"?