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

[Samiullah Khawaja <skhawaja@google.com>]

On Tue, Apr 28, 2026 at 05:24:53PM +0000, Samiullah Khawaja wrote:
>On Thu, Apr 23, 2026 at 09:23:06PM +0000, David Matlack 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/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.

nit: I was wondering why is this named refcount and why it is needed. It
seems you are using it to track the preservation dependency between
parent devices and leaf. Maybe add a comment to clarify that.
>> */
>>struct pci_dev_ser {
>>	u32 domain;
>>	u16 bdf;
>>-	u16 reserved;
>>+	u16 refcount;
>>} __packed;
>>
>>/**

Sami