[PATCH v6 02/12] PCI: liveupdate: Track outgoing preserved PCI devices
David Matlack
dmatlack at google.com
Fri May 22 13:24:00 PDT 2026
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 at google.com>
---
drivers/pci/liveupdate.c | 167 +++++++++++++++++++++++++++++++++
drivers/pci/liveupdate.h | 21 +++++
drivers/pci/probe.c | 2 +
include/linux/kho/abi/pci.h | 9 +-
include/linux/pci.h | 3 +
include/linux/pci_liveupdate.h | 21 +++++
6 files changed, 220 insertions(+), 3 deletions(-)
create mode 100644 drivers/pci/liveupdate.h
diff --git a/drivers/pci/liveupdate.c b/drivers/pci/liveupdate.c
index 737e7b9366db..065d5af822f7 100644
--- a/drivers/pci/liveupdate.c
+++ b/drivers/pci/liveupdate.c
@@ -36,6 +36,26 @@
*
* * ``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 its 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
@@ -48,6 +68,21 @@
#include <linux/mm.h>
#include <linux/pci.h>
+#include "liveupdate.h"
+
+/**
+ * struct pci_liveupdate_global - Global state for PCI Live Update support
+ * @rwsem: Reader/writer semaphore used to protect the incoming and outgoing
+ * FLBs, and the references to them in struct pci_dev.
+ */
+struct pci_liveupdate_global {
+ struct rw_semaphore rwsem;
+};
+
+static struct pci_liveupdate_global pci_liveupdate = {
+ .rwsem = __RWSEM_INITIALIZER(pci_liveupdate.rwsem),
+};
+
static int pci_flb_preserve(struct liveupdate_flb_op_args *args)
{
struct pci_dev *dev = NULL;
@@ -115,6 +150,138 @@ static struct liveupdate_flb pci_liveupdate_flb = {
.compatible = PCI_LUO_FLB_COMPATIBLE,
};
+static struct pci_ser *pci_liveupdate_flb_get_outgoing(void)
+{
+ struct pci_ser *ser = NULL;
+ int ret;
+
+ ret = liveupdate_flb_get_outgoing(&pci_liveupdate_flb, (void **)&ser);
+ if (ret)
+ return ERR_PTR(ret);
+
+ if (!ser)
+ return ERR_PTR(-ENOENT);
+
+ return ser;
+}
+
+static void pci_liveupdate_unpreserve_device(struct pci_ser *ser, struct pci_dev *dev)
+{
+ struct pci_dev_ser *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;
+}
+
+static int pci_liveupdate_preserve_device(struct pci_ser *ser, struct pci_dev *dev)
+{
+ int i;
+
+ 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;
+}
+
+/**
+ * pci_liveupdate_preserve() - Preserve a PCI device across Live Update
+ * @dev: The PCI device to preserve.
+ *
+ * pci_liveupdate_preserve() notifies the PCI core that a PCI device should be
+ * preserved across the next Live Update. Drivers are expected to call
+ * pci_liveupdate_preserve() from their struct liveupdate_file_handler
+ * preserve() callback to ensure the outgoing struct pci_ser is already set up.
+ *
+ * Returns: 0 on success, <0 on failure.
+ */
+int pci_liveupdate_preserve(struct pci_dev *dev)
+{
+ struct pci_ser *ser = NULL;
+
+ if (dev->is_virtfn)
+ return -EINVAL;
+
+ guard(rwsem_write)(&pci_liveupdate.rwsem);
+
+ ser = pci_liveupdate_flb_get_outgoing();
+ if (IS_ERR(ser))
+ return PTR_ERR(ser);
+
+ return pci_liveupdate_preserve_device(ser, dev);
+}
+EXPORT_SYMBOL_GPL(pci_liveupdate_preserve);
+
+/**
+ * pci_liveupdate_unpreserve() - Cancel preservation of a PCI device
+ * @dev: The PCI device to unpreserve.
+ *
+ * pci_liveupdate_unpreserve() notifies the PCI core that a PCI device should no
+ * longer be preserved across the next Live Update. Drivers are expected to call
+ * pci_liveupdate_unpreserve() from their struct liveupdate_file_handler
+ * unpreserve() callback to ensure the outgoing struct pci_ser is already set
+ * up.
+ */
+void pci_liveupdate_unpreserve(struct pci_dev *dev)
+{
+ struct pci_ser *ser = NULL;
+
+ guard(rwsem_write)(&pci_liveupdate.rwsem);
+
+ ser = pci_liveupdate_flb_get_outgoing();
+ if (IS_ERR(ser)) {
+ pci_warn(dev, "Cannot unpreserve device without outgoing Live Update state\n");
+ return;
+ }
+
+ pci_liveupdate_unpreserve_device(ser, dev);
+}
+EXPORT_SYMBOL_GPL(pci_liveupdate_unpreserve);
+
+void pci_liveupdate_cleanup_device(struct pci_dev *dev)
+{
+ /*
+ * It should be safe to READ_ONCE() outside of the rwsem during cleanup
+ * since there should no longer be any references to @dev on the system.
+ */
+ if (READ_ONCE(dev->liveupdate.outgoing)) {
+ pci_WARN(dev, 1, "Destroying outgoing-preserved device!\n");
+ pci_liveupdate_unpreserve(dev);
+ }
+}
+
/**
* pci_liveupdate_register_flb() - Register a file handler with the PCI core
* @fh: The file handler to register.
diff --git a/drivers/pci/liveupdate.h b/drivers/pci/liveupdate.h
new file mode 100644
index 000000000000..b2335581f8d0
--- /dev/null
+++ b/drivers/pci/liveupdate.h
@@ -0,0 +1,21 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * PCI Live Update support (core API)
+ *
+ * Copyright (c) 2026, Google LLC.
+ * David Matlack <dmatlack at google.com>
+ */
+#ifndef DRIVERS_PCI_LIVEUPDATE_H
+#define DRIVERS_PCI_LIVEUPDATE_H
+
+#include <linux/pci.h>
+
+#ifdef CONFIG_PCI_LIVEUPDATE
+void pci_liveupdate_cleanup_device(struct pci_dev *dev);
+#else
+static inline void pci_liveupdate_cleanup_device(struct pci_dev *dev)
+{
+}
+#endif
+
+#endif /* DRIVERS_PCI_LIVEUPDATE_H */
diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index b63cd0c310bc..b88109a8dfe4 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -24,6 +24,7 @@
#include <linux/pm_runtime.h>
#include <linux/bitfield.h>
#include <trace/events/pci.h>
+#include "liveupdate.h"
#include "pci.h"
static struct resource busn_resource = {
@@ -2490,6 +2491,7 @@ static void pci_release_dev(struct device *dev)
pci_dev = to_pci_dev(dev);
pci_release_capabilities(pci_dev);
+ pci_liveupdate_cleanup_device(pci_dev);
pci_release_of_node(pci_dev);
pcibios_release_device(pci_dev);
pci_bus_put(pci_dev->bus);
diff --git a/include/linux/kho/abi/pci.h b/include/linux/kho/abi/pci.h
index 6ebcf817fff4..85def616703d 100644
--- a/include/linux/kho/abi/pci.h
+++ b/include/linux/kho/abi/pci.h
@@ -23,19 +23,22 @@
* 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.
- * @padding: Padding 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. The value of the
+ * refcount is equal to 1 when the struct pci_dev_ser is in use, and
+ * 0 otherwise.
*/
struct pci_dev_ser {
u32 domain;
u16 bdf;
- u16 padding;
+ u16 refcount;
} __packed;
/**
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 8cadeeab86fd..a7c3722b1e77 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -594,6 +594,9 @@ struct pci_dev {
u8 tph_mode; /* TPH mode */
u8 tph_req_type; /* TPH requester type */
#endif
+#ifdef CONFIG_PCI_LIVEUPDATE
+ struct pci_liveupdate liveupdate;
+#endif
};
static inline struct pci_dev *pci_physfn(struct pci_dev *dev)
diff --git a/include/linux/pci_liveupdate.h b/include/linux/pci_liveupdate.h
index 8ec98beefcb4..cfcfbfa73af7 100644
--- a/include/linux/pci_liveupdate.h
+++ b/include/linux/pci_liveupdate.h
@@ -8,14 +8,26 @@
#ifndef LINUX_PCI_LIVEUPDATE_H
#define LINUX_PCI_LIVEUPDATE_H
+#include <linux/kho/abi/pci.h>
#include <linux/liveupdate.h>
#include <linux/types.h>
+#include <linux/spinlock_types.h>
+
+/**
+ * struct pci_liveupdate - PCI Live Update state for a struct pci_dev
+ * @outgoing: State preserved for the next kernel.
+ */
+struct pci_liveupdate {
+ struct pci_dev_ser *outgoing;
+};
struct pci_dev;
#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);
#else
static inline int pci_liveupdate_register_flb(struct liveupdate_file_handler *fh)
{
@@ -25,6 +37,15 @@ 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)
+{
+}
#endif
#endif /* LINUX_PCI_LIVEUPDATE_H */
--
2.54.0.746.g67dd491aae-goog
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