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

Jacob Pan
2026-04-27T15:57:28Z

Hi David,

On Thu, 23 Apr 2026 21:23:06 +0000
David Matlack <dmatlack@google.com> wrote:

> 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;
This can be left outside the mutex?

> +
> + 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 */