Re: [PATCH v3 02/24] PCI: Add API to track PCI devices preserved across Live Update

Zhu Yanjun
2026-04-05T16:56:51Z

在 2026/4/3 14:58, David Matlack 写道:
> On Thu, Apr 2, 2026 at 2:29 PM Yanjun.Zhu <yanjun.zhu@linux.dev> wrote:
>> On 3/23/26 4:57 PM, David Matlack wrote:
>>> +config PCI_LIVEUPDATE
>>> + bool "PCI Live Update Support (EXPERIMENTAL)"
>>> + depends on PCI && LIVEUPDATE
>>> + help
>>> + Support for preserving PCI devices across a Live Update. This option
>>> + should only be enabled by developers working on implementing this
>>> + support. Once enough support as landed in the kernel, this option
>>> + will no longer be marked EXPERIMENTAL.
>>> +
>>> + If unsure, say N.
>> Currently, it only supports 'n' or 'y'. Is it possible to add 'm'
>> (modular support)?
>>
>> This would allow the feature to be built as a kernel module. For
>> development
>>
>> purposes, modularization means we only need to recompile a single module
>>
>> for testing, rather than rebuilding the entire kernel. Compiling a
>> module should
>>
>> be significantly faster than a full kernel build.
> I don't think it is possible for CONFIG_PCI_LIVEUPDATE to support 'm'.
> pci_setup_device() (which is under CONFIG_PCI) needs to call
> pci_liveupdate_setup_device(), and CONFIG_PCI cannot be built as a
> module. This call is necessary so the PCI core knows whether a device
> being enumerated was preserved across a previous Live Update.

After the following changes, the liveupdate.ko can be generated
successfully.

"

# ls drivers/pci/liveupdate.ko
drivers/pci/liveupdate.ko
"

diff --git a/drivers/pci/Kconfig b/drivers/pci/Kconfig

index 05307d89c3f4..e172c31b33fa 100644
--- a/drivers/pci/Kconfig
+++ b/drivers/pci/Kconfig
@@ -335,7 +335,7 @@ config VGA_ARB_MAX_GPUS
multiple GPUS.  The overhead for each GPU is very small.

config PCI_LIVEUPDATE
-       bool "PCI Live Update Support (EXPERIMENTAL)"
+       tristate "PCI Live Update Support (EXPERIMENTAL)"
depends on PCI && LIVEUPDATE
help
Support for preserving PCI devices across a Live Update. This
option
diff --git a/drivers/pci/liveupdate.c b/drivers/pci/liveupdate.c
index c1251f4f8438..71bab8ecba85 100644
--- a/drivers/pci/liveupdate.c
+++ b/drivers/pci/liveupdate.c
@@ -413,3 +413,26 @@ void pci_liveupdate_unregister_flb(struct
liveupdate_file_handler *fh)
liveupdate_unregister_flb(fh, &pci_liveupdate_flb);
}
EXPORT_SYMBOL_GPL(pci_liveupdate_unregister_flb);
+
+extern void (*pci_liveupdate_setup_device_hook)(struct pci_dev *dev);
+extern u32 (*pci_liveupdate_incoming_nr_devices_hook)(void);
+static int __init liveupdate_module_init(void)
+{
+       pci_liveupdate_setup_device_hook = pci_liveupdate_setup_device;
+       pci_liveupdate_incoming_nr_devices_hook =
pci_liveupdate_incoming_nr_devices;
+       pr_info("loaded\n");
+       return 0;
+}
+
+static void __exit liveupdate_module_exit(void)
+{
+       pci_liveupdate_setup_device_hook = NULL;
+       pci_liveupdate_incoming_nr_devices_hook = NULL;
+       pr_info("unloaded\n");
+}
+
+module_init(liveupdate_module_init);
+module_exit(liveupdate_module_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("PCI Live Update Support");
diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index 979cb9921340..93f76500cb0d 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -1434,18 +1434,12 @@ static inline int pci_msix_write_tph_tag(struct
pci_dev *pdev, unsigned int inde
(PCI_CONF1_ADDRESS(bus, dev, func, reg) | \
PCI_CONF1_EXT_REG(reg))

-#ifdef CONFIG_PCI_LIVEUPDATE
+#if IS_ENABLED(CONFIG_PCI_LIVEUPDATE)
void pci_liveupdate_setup_device(struct pci_dev *dev);
-u32 pci_liveupdate_incoming_nr_devices(void);
#else
static inline void pci_liveupdate_setup_device(struct pci_dev *dev)
{
}
-
-static inline u32 pci_liveupdate_incoming_nr_devices(void)
-{
-       return 0;
-}
#endif

#endif /* DRIVERS_PCI_H */
diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 165056d71e66..4880302bca43 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -1369,6 +1369,9 @@ bool pci_ea_fixed_busnrs(struct pci_dev *dev, u8
*sec, u8 *sub)
return true;
}

+u32 (*pci_liveupdate_incoming_nr_devices_hook)(void) = NULL;
+EXPORT_SYMBOL_GPL(pci_liveupdate_incoming_nr_devices_hook);
+
static bool pci_assign_all_busses(void)
{
if (!pcibios_assign_all_busses())
@@ -1389,7 +1392,7 @@ static bool pci_assign_all_busses(void)
* numbers during the initial cold boot, and then that topology
would
* then remain fixed across any subsequent Live Updates.
*/
-       if (pci_liveupdate_incoming_nr_devices()) {
+       if (pci_liveupdate_incoming_nr_devices_hook &&
pci_liveupdate_incoming_nr_devices_hook()) {
pr_info_once("Ignoring pci=assign-busses and inheriting
bus numbers during Live Update\n");
return false;
}
@@ -2030,6 +2033,9 @@ static const char *pci_type_str(struct pci_dev *dev)
}
}

+void (*pci_liveupdate_setup_device_hook)(struct pci_dev *dev) = NULL;
+EXPORT_SYMBOL_GPL(pci_liveupdate_setup_device_hook);
+
/**
* pci_setup_device - Fill in class and map information of a device
* @dev: the device structure to fill
@@ -2091,7 +2097,8 @@ int pci_setup_device(struct pci_dev *dev)
if (pci_early_dump)
early_dump_pci_device(dev);

-       pci_liveupdate_setup_device(dev);
+       if (pci_liveupdate_setup_device_hook)
+               pci_liveupdate_setup_device_hook(dev);

/* Need to have dev->class ready */
dev->cfg_size = pci_cfg_space_size(dev);
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 27ee9846a2fd..aaab6adb487e 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -592,7 +592,7 @@ struct pci_dev {
u8              tph_mode;       /* TPH mode */
u8              tph_req_type;   /* TPH requester type */
#endif
-#ifdef CONFIG_PCI_LIVEUPDATE
+#if IS_ENABLED(CONFIG_PCI_LIVEUPDATE)
unsigned int    liveupdate_incoming:1;  /* Preserved by
previous kernel */
unsigned int    liveupdate_outgoing:1;  /* Preserved for next
kernel */
#endif
@@ -2876,7 +2876,7 @@ void pci_uevent_ers(struct pci_dev *pdev, enum
pci_ers_result err_type);
WARN_ONCE(condition, "%s %s: " fmt, \
dev_driver_string(&(pdev)->dev), pci_name(pdev), ##arg)

-#ifdef CONFIG_PCI_LIVEUPDATE
+#if IS_ENABLED(CONFIG_PCI_LIVEUPDATE)
int pci_liveupdate_preserve(struct pci_dev *dev);
void pci_liveupdate_unpreserve(struct pci_dev *dev);
int pci_liveupdate_retrieve(struct pci_dev *dev);
diff --git a/kernel/liveupdate/luo_flb.c b/kernel/liveupdate/luo_flb.c
index 874830f8e44d..33fbdc6c417c 100644
--- a/kernel/liveupdate/luo_flb.c
+++ b/kernel/liveupdate/luo_flb.c
@@ -461,7 +461,7 @@ int liveupdate_register_flb(struct
liveupdate_file_handler *fh,

return 0;
}
-
+EXPORT_SYMBOL_GPL(liveupdate_register_flb);
/**
* liveupdate_unregister_flb - Remove an FLB dependency from a file
handler.
* @fh:   The file handler that is currently depending on the FLB.
@@ -487,7 +487,7 @@ void liveupdate_unregister_flb(struct
liveupdate_file_handler *fh,

luo_flb_unregister_one(fh, flb);
}
-
+EXPORT_SYMBOL_GPL(liveupdate_unregister_flb);
/**
* liveupdate_flb_get_incoming - Retrieve the incoming FLB object.
* @flb:  The FLB definition.
@@ -525,7 +525,7 @@ int liveupdate_flb_get_incoming(struct
liveupdate_flb *flb, void **objp)

return 0;
}
-
+EXPORT_SYMBOL_GPL(liveupdate_flb_get_incoming);
/**
* liveupdate_flb_get_outgoing - Retrieve the outgoing FLB object.
* @flb:  The FLB definition.
@@ -552,6 +552,7 @@ int liveupdate_flb_get_outgoing(struct
liveupdate_flb *flb, void **objp)

return 0;
}
+EXPORT_SYMBOL_GPL(liveupdate_flb_get_outgoing);

int __init luo_flb_setup_outgoing(void *fdt_out)
{

--
Best Regards,
Yanjun.Zhu