Merge patch series "PCI: liveupdate: PCI core support for Live Update"

David Matlack <dmatlack@google.com> says:

This series introduces support in the PCI core for Live Update, enabling
drivers to preserve PCI devices across a kexec-based kernel update
without interrupting the device. This functionality is critical for
minimizing downtime in environments where PCI devices (e.g., those
assigned to VMs via VFIO) must continue operating or maintain state
across a host kernel upgrade.

Specifically, this series allows preserved PCI devices to perform
uninterrupted memory transactions (DMA) targeting system memory
(specifically, preserved memfds) across a Live Update. These devices can
be behind a bridge but must not be VFs. Support for P2P and VF
preservation will be addressed in future series.

Link: https://patch.msgid.link/20260918200640.887030-1-dmatlack@google.com
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>

3 files changed, 145 insertions, 0 deletions

diff --git a/include/linux/kho/abi/pci.h b/include/linux/kho/abi/pci.h
new file mode 100644
index 000000000000..9485ed73c351
--- /dev/null
+++ b/include/linux/kho/abi/pci.h
@@ -0,0 +1,66 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+/*
+ * Copyright (c) 2026, Google LLC.
+ * David Matlack <dmatlack@google.com>
+ */
+
+#ifndef _LINUX_KHO_ABI_PCI_H
+#define _LINUX_KHO_ABI_PCI_H
+
+#include <linux/bug.h>
+#include <linux/compiler.h>
+#include <linux/types.h>
+
+/**
+ * DOC: PCI File-Lifecycle Bound (FLB) Live Update ABI
+ *
+ * This header defines the ABI for preserving core PCI state across kexec using
+ * Live Update File-Lifecycle Bound (FLB) data.
+ *
+ * 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 PCI_LUO_FLB_VERSION number.
+ */
+
+#define PCI_LUO_FLB_COMPATIBLE "pci"
+#define PCI_LUO_FLB_VERSION 2
+
+/**
+ * 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.
+ * @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 the number of preserved devices at or below
+ *            it in the PCI hierarchy when the struct pci_dev_ser is in use, and
+ *            0 otherwise.
+ */
+struct pci_dev_ser {
+	u32 domain;
+	u16 bdf;
+	u16 refcount;
+} __packed;
+
+/**
+ * struct pci_ser - PCI Subsystem Live Update State
+ *
+ * This struct tracks state about all devices that are being preserved across
+ * a Live Update for the next kernel. It contains only state owned by the PCI
+ * core; the state a driver needs to resume its device is preserved separately
+ * by that driver.
+ *
+ * @version: The version of the "pci" FLB struct. This field must never be
+ *           deleted, moved, or resized, as the kernel depends on always being
+ *           able to check the struct pci_ser version number.
+ * @nr_devices: The number of devices that were preserved.
+ * @devices: Physical address of the first KHO block containing pci_dev_ser.
+ */
+struct pci_ser {
+	u32 version;
+	u32 nr_devices;
+	u64 devices;
+} __packed;
+
+#endif /* _LINUX_KHO_ABI_PCI_H */
diff --git a/include/linux/pci.h b/include/linux/pci.h
index d31a8d107b1e..b35ac263c451 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -43,6 +43,7 @@
 #include <uapi/linux/pci.h>
 
 #include <linux/pci_ids.h>
+#include <linux/pci_liveupdate.h>
 
 #define PCI_STATUS_ERROR_BITS (PCI_STATUS_DETECTED_PARITY  | \
 			       PCI_STATUS_SIG_SYSTEM_ERROR | \
@@ -598,6 +599,9 @@ 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)
@@ -832,6 +836,9 @@ static inline struct pci_dev *pci_upstream_bridge(struct pci_dev *dev)
 	return dev->bus->self;
 }
 
+#define for_each_pci_dev_in_path(dev) \
+	for (; dev; dev = pci_upstream_bridge(dev))
+
 #ifdef CONFIG_PCI_MSI
 static inline bool pci_dev_msi_enabled(struct pci_dev *pci_dev)
 {
diff --git a/include/linux/pci_liveupdate.h b/include/linux/pci_liveupdate.h
new file mode 100644
index 000000000000..bb79348769b7
--- /dev/null
+++ b/include/linux/pci_liveupdate.h
@@ -0,0 +1,72 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * PCI Live Update support (Public/Driver API)
+ *
+ * Copyright (c) 2026, Google LLC.
+ * David Matlack <dmatlack@google.com>
+ */
+#ifndef LINUX_PCI_LIVEUPDATE_H
+#define LINUX_PCI_LIVEUPDATE_H
+
+#include <linux/kho/abi/pci.h>
+#include <linux/liveupdate.h>
+#include <linux/spinlock_types.h>
+#include <linux/types.h>
+
+/**
+ * struct pci_liveupdate - PCI Live Update state for a struct pci_dev
+ * @outgoing: State preserved for the next kernel.
+ * @incoming: State preserved by the previous kernel.
+ * @was_incoming: True if this struct pci_dev was incoming-preserved when it was
+ *                set up, i.e. it was matched to state preserved by the previous
+ *                kernel. Unlike @incoming, this is never cleared, so it stays
+ *                true after the device finishes participating in Live Update.
+ * @frozen: True if the outgoing preservation status of this device is frozen
+ *          and thus cannot be changed.
+ */
+struct pci_liveupdate {
+	struct pci_dev_ser *outgoing;
+	struct pci_dev_ser *incoming;
+	bool was_incoming;
+	bool frozen;
+};
+
+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);
+void pci_liveupdate_finish(struct pci_dev *dev);
+bool pci_liveupdate_is_incoming(struct pci_dev *dev);
+#else
+static inline int pci_liveupdate_register_flb(struct liveupdate_file_handler *fh)
+{
+	return -EOPNOTSUPP;
+}
+
+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 void pci_liveupdate_finish(struct pci_dev *dev)
+{
+}
+
+static inline bool pci_liveupdate_is_incoming(struct pci_dev *dev)
+{
+	return false;
+}
+#endif
+
+#endif /* LINUX_PCI_LIVEUPDATE_H */