Re: [PATCH v6 03/12] PCI: liveupdate: Track incoming preserved PCI devices

[Samiullah Khawaja <skhawaja@google.com>]

On Fri, May 22, 2026 at 08:24:01PM +0000, David Matlack wrote:
>During PCI enumeration, the previous kernel might have passed state about
>devices that were preserved across kexec. The PCI core needs to fetch
>this state to identify which devices are "incoming" and require special
>handling.
>
>Add pci_liveupdate_setup_device() which is called during device setup
>to fetch the serialized state (struct pci_ser) from the Live Update
>Orchestrator. The first time this happens, pci_flb_retrieve() will run
>and convert the array of pci_dev_ser structs into an xarray so that it
>can be looked up efficiently.
>
>If a device is found in the xarray, the PCI core stores a pointer to its
>state in dev->liveupdate_incoming and holds a reference to the incoming
>FLB until pci_liveupdate_finish() is called by the driver.
>
>This ensures proper lifecycle management for incoming preserved devices
>and allows the PCI core and drivers to apply specific Live Update
>logic to them in subsequent commits.
>
>Drivers can check if a device is an incoming preserved device (e.g.
>during probe) by calling pci_liveupdate_is_incoming().
>
>CONFIG_64BIT is now required to enable CONFIG_PCI_LIVEUPDATE so that the
>domain and bdf can be guaranteed to fit in an unsigned long and be used
>as the xarray key.
>
>Signed-off-by: David Matlack <dmatlack@google.com>
>---
> MAINTAINERS                    |   1 +
> drivers/pci/Kconfig            |   2 +-
> drivers/pci/liveupdate.c       | 230 ++++++++++++++++++++++++++++++++-
> drivers/pci/liveupdate.h       |   5 +
> drivers/pci/probe.c            |   3 +
> include/linux/pci_liveupdate.h |  13 ++
> 6 files changed, 251 insertions(+), 3 deletions(-)
>

[snip]
>
> static int pci_flb_retrieve(struct liveupdate_flb_op_args *args)
> {
>-	args->obj = phys_to_virt(args->data);
>+	struct pci_ser *ser = phys_to_virt(args->data);
>+	struct pci_flb_incoming *incoming;
>+	int ret = -ENOMEM;
>+	u32 i;
>+
>+	incoming = kmalloc_obj(*incoming);
>+	if (!incoming)
>+		goto err_restore_free;
>+
>+	incoming->ser = ser;
>+	xa_init(&incoming->xa);
>+
>+	for (i = 0; i < incoming->ser->max_nr_devices; i++) {
>+		struct pci_dev_ser *dev_ser = &incoming->ser->devices[i];
>+		unsigned long key;
>+
>+		if (!dev_ser->refcount)
>+			continue;
>+
>+		key = pci_ser_xa_key(dev_ser->domain, dev_ser->bdf);
>+		ret = xa_insert(&incoming->xa, key, dev_ser, GFP_KERNEL);
>+		if (ret)
>+			goto err_xa_destroy;
>+	}
>+
>+	args->obj = incoming;
> 	return 0;
>+
>+err_xa_destroy:
>+	xa_destroy(&incoming->xa);
>+	kfree(incoming);
>+err_restore_free:
>+	kho_restore_free(ser);
>+	return ret;

Hmm.. This is interesting, so the KHO state is freed and it cannot be
reused. I see you already pointed out that we are putting an LUO policy
to say that the retry is not allowed.

But what should be the behaviour of liveupdate in this regard? Let the
system boot in a normal way? This might break other subsystems as they
might depend on PCIe restoring state properly. Also I think some of the
PCIe state, like device-id, BAR addresses, ACLs etc, might be used as
source of truth by other components.

For example, lets say FLB retrieve() of PCIe fails, but succeeds for
VFIO/IOMMU, now VFIO/IOMMU are restoring state of a device that is not
restored/preserved?

Should this be considered fatal?
> }
>
> static void pci_flb_finish(struct liveupdate_flb_op_args *args)
> {
>-	kho_restore_free(args->obj);
>+	struct pci_flb_incoming *incoming = args->obj;
>+
>+	xa_destroy(&incoming->xa);
>+	kho_restore_free(incoming->ser);
>+	kfree(incoming);
> }
>
> static struct liveupdate_flb_ops pci_liveupdate_flb_ops = {
>@@ -270,6 +335,91 @@ void pci_liveupdate_unpreserve(struct pci_dev *dev)
> }
> EXPORT_SYMBOL_GPL(pci_liveupdate_unpreserve);
>
>+static struct pci_flb_incoming *pci_liveupdate_flb_get_incoming(void)
>+{
>+	struct pci_flb_incoming *incoming = NULL;
>+	int ret;
>+
>+	ret = liveupdate_flb_get_incoming(&pci_liveupdate_flb, (void **)&incoming);
>+
>+	/* Live Update is not enabled. */
>+	if (ret == -EOPNOTSUPP)
>+		return NULL;
>+
>+	/* Live Update is enabled, but there is no incoming FLB data. */
>+	if (ret == -ENODATA)
>+		return NULL;
>+
>+	/*
>+	 * Live Update is enabled and there is incoming FLB data, but none of it
>+	 * matches pci_liveupdate_flb.compatible.
>+	 *
>+	 * This could mean that no PCI FLB data was passed by the previous
>+	 * kernel, but it could also mean the previous kernel used a different
>+	 * compatibility string (i.e. a different ABI).
>+	 */
>+	if (ret == -ENOENT) {
>+		pr_info_once("No incoming FLB matched %s\n", pci_liveupdate_flb.compatible);
>+		return NULL;
>+	}
>+
>+	/*
>+	 * There is incoming FLB data that matches pci_liveupdate_flb.compatible
>+	 * but it cannot be retrieved.
>+	 */
>+	if (ret) {
>+		WARN_ONCE(ret, "Failed to retrieve incoming FLB data\n");

I think this should probably be considered fatal as mentioned above or
the caller of this function should get an error so it can fail. I think
retrievel of preserved state should generally not fail unless there is
memory corruption or ABI is incompatible.
>+		return NULL;
>+	}
>+
>+	return incoming;
>+}
>+

[snip]
>+
>+static inline bool pci_liveupdate_is_incoming(struct pci_dev *dev)
>+{
>+	return false;
>+}
> #endif
>
> #endif /* LINUX_PCI_LIVEUPDATE_H */
>-- 
>2.54.0.746.g67dd491aae-goog
>

Sami