[PATCH v4 02/11] PCI: liveupdate: Track outgoing preserved PCI devices

David Matlack
2026-04-23T21:23:29Z

Add APIs to allow drivers to notify the PCI core of which devices are
being preserved across a Live Update for the next kernel, i.e.
"outgoing" devices.

Drivers must notify the PCI core when devices are preserved so that the
PCI core can update its FLB data (struct pci_ser) and track the list of
outgoing devices. pci_liveupdate_preserve() notifies the PCI core that a
device must be preserved across Live Update. pci_liveupdate_unpreserve()
reverses this (cancels the preservation of the device).

This tracking ensures the PCI core is fully aware of which devices may
need special handling during shutdown and kexec, and so that it can be
handed off to the next kernel.

Signed-off-by: David Matlack <dmatlack@google.com>
---
drivers/pci/liveupdate.c | 101 ++++++++++++++++++++++++++++++++++++
include/linux/kho/abi/pci.h | 7 +--
include/linux/pci.h | 26 ++++++++++
3 files changed, 131 insertions(+), 3 deletions(-)

diff --git a/drivers/pci/liveupdate.c b/drivers/pci/liveupdate.c
index d4fa61625d56..2dd8daa2f17c 100644
--- a/drivers/pci/liveupdate.c
+++ b/drivers/pci/liveupdate.c
@@ -43,6 +43,26 @@
*
* * ``pci_liveupdate_register_flb(driver_file_handler)``
* * ``pci_liveupdate_unregister_flb(driver_file_handler)``
+ *
+ * Device Tracking
+ * ===============
+ *
+ * Drivers must notify the PCI core when specific devices are preserved or
+ * unpreserved with the following APIs:
+ *
+ * * ``pci_liveupdate_preserve(pci_dev)``
+ * * ``pci_liveupdate_unpreserve(pci_dev)``
+ *
+ * This allows the PCI core to keep it's FLB data (struct pci_ser) up to date
+ * with the list of **outgoing** preserved devices for the next kernel.
+ *
+ * Restrictions
+ * ============
+ *
+ * The PCI core enforces the following restrictions on which devices can be
+ * preserved. These may be relaxed in the future:
+ *
+ * * The device cannot be a Virtual Function (VF).
*/

#define pr_fmt(fmt) "PCI: liveupdate: " fmt
@@ -57,6 +77,8 @@
#include <linux/pci.h>
#include <linux/sort.h>

+static DEFINE_MUTEX(pci_flb_outgoing_lock);
+
static int pci_flb_preserve(struct liveupdate_flb_op_args *args)
{
struct pci_dev *dev = NULL;
@@ -124,6 +146,85 @@ static struct liveupdate_flb pci_liveupdate_flb = {
.compatible = PCI_LUO_FLB_COMPATIBLE,
};

+int pci_liveupdate_preserve(struct pci_dev *dev)
+{
+ struct pci_ser *ser;
+ int i, ret;
+
+ guard(mutex)(&pci_flb_outgoing_lock);
+
+ ret = liveupdate_flb_get_outgoing(&pci_liveupdate_flb, (void **)&ser);
+ if (ret)
+ return ret;
+
+ if (!ser)
+ return -ENOENT;
+
+ if (dev->is_virtfn)
+ return -EINVAL;
+
+ if (dev->liveupdate_outgoing)
+ return -EBUSY;
+
+ if (ser->nr_devices == ser->max_nr_devices)
+ return -ENOSPC;
+
+ for (i = 0; i < ser->max_nr_devices; i++) {
+ /*
+ * Start searching at index ser->nr_devices. This should result
+ * in a constant time search under expected conditions (devices
+ * are not getting unpreserved).
+ */
+ int index = (ser->nr_devices + i) % ser->max_nr_devices;
+ struct pci_dev_ser *dev_ser = &ser->devices[index];
+
+ if (dev_ser->refcount)
+ continue;
+
+ pci_info(dev, "Device will be preserved across next Live Update\n");
+ ser->nr_devices++;
+
+ dev_ser->domain = pci_domain_nr(dev->bus);
+ dev_ser->bdf = pci_dev_id(dev);
+ dev_ser->refcount = 1;
+
+ dev->liveupdate_outgoing = dev_ser;
+ return 0;
+ }
+
+ return -ENOSPC;
+}
+EXPORT_SYMBOL_GPL(pci_liveupdate_preserve);
+
+void pci_liveupdate_unpreserve(struct pci_dev *dev)
+{
+ struct pci_dev_ser *dev_ser;
+ struct pci_ser *ser = NULL;
+ int ret;
+
+ guard(mutex)(&pci_flb_outgoing_lock);
+
+ ret = liveupdate_flb_get_outgoing(&pci_liveupdate_flb, (void **)&ser);
+
+ if (ret || !ser) {
+ pci_warn(dev, "Cannot unpreserve device without outgoing Live Update state\n");
+ return;
+
+ }
+
+ dev_ser = dev->liveupdate_outgoing;
+ if (!dev_ser) {
+ pci_warn(dev, "Cannot unpreserve device that is not preserved\n");
+ return;
+ }
+
+ pci_info(dev, "Device will no longer be preserved across next Live Update\n");
+ ser->nr_devices--;
+ memset(dev_ser, 0, sizeof(*dev_ser));
+ dev->liveupdate_outgoing = NULL;
+}
+EXPORT_SYMBOL_GPL(pci_liveupdate_unpreserve);
+
int pci_liveupdate_register_flb(struct liveupdate_file_handler *fh)
{
pr_debug("Registering file handler \"%s\"\n", fh->compatible);
diff --git a/include/linux/kho/abi/pci.h b/include/linux/kho/abi/pci.h
index 5c0e92588c00..5b4c8d9e462c 100644
--- a/include/linux/kho/abi/pci.h
+++ b/include/linux/kho/abi/pci.h
@@ -23,19 +23,20 @@
* incrementing the version number in the PCI_LUO_FLB_COMPATIBLE string.
*/

-#define PCI_LUO_FLB_COMPATIBLE "pci-v1"
+#define PCI_LUO_FLB_COMPATIBLE "pci-v2"

/**
* struct pci_dev_ser - Serialized state about a single PCI device.
*
* @domain: The device's PCI domain number (segment).
* @bdf: The device's PCI bus, device, and function number.
- * @reserved: Reserved (to naturally align struct pci_dev_ser).
+ * @refcount: Reference count used by the PCI core to keep track of whether it
+ * is done using a device's struct pci_dev_ser.
*/
struct pci_dev_ser {
u32 domain;
u16 bdf;
- u16 reserved;
+ u16 refcount;
} __packed;

/**
diff --git a/include/linux/pci.h b/include/linux/pci.h
index d70080babd52..eb94cbd8ab9d 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -41,6 +41,7 @@
#include <linux/msi_api.h>
#include <uapi/linux/pci.h>
#include <linux/liveupdate.h>
+#include <linux/kho/abi/pci.h>

#include <linux/pci_ids.h>

@@ -594,6 +595,9 @@ struct pci_dev {
u8 tph_mode; /* TPH mode */
u8 tph_req_type; /* TPH requester type */
#endif
+#ifdef CONFIG_PCI_LIVEUPDATE
+ struct pci_dev_ser *liveupdate_outgoing; /* State preserved for next kernel */
+#endif
};

static inline struct pci_dev *pci_physfn(struct pci_dev *dev)
@@ -2880,6 +2884,14 @@ void pci_uevent_ers(struct pci_dev *pdev, enum pci_ers_result err_type);
#ifdef CONFIG_PCI_LIVEUPDATE
int pci_liveupdate_register_flb(struct liveupdate_file_handler *fh);
void pci_liveupdate_unregister_flb(struct liveupdate_file_handler *fh);
+
+int pci_liveupdate_preserve(struct pci_dev *dev);
+void pci_liveupdate_unpreserve(struct pci_dev *dev);
+
+static inline struct pci_dev_ser *pci_liveupdate_outgoing(struct pci_dev *dev)
+{
+ return dev->liveupdate_outgoing;
+}
#else
static inline int pci_liveupdate_register_flb(struct liveupdate_file_handler *fh)
{
@@ -2889,6 +2901,20 @@ static inline int pci_liveupdate_register_flb(struct liveupdate_file_handler *fh
static inline void pci_liveupdate_unregister_flb(struct liveupdate_file_handler *fh)
{
}
+
+static inline int pci_liveupdate_preserve(struct pci_dev *dev)
+{
+ return -EOPNOTSUPP;
+}
+
+static inline void pci_liveupdate_unpreserve(struct pci_dev *dev)
+{
+}
+
+static inline struct pci_dev_ser *pci_liveupdate_outgoing(struct pci_dev *dev)
+{
+ return NULL;
+}
#endif

#endif /* LINUX_PCI_H */
--
2.54.0.rc2.544.gc7ae2d5bb8-goog