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

[Samiullah Khawaja]

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@xxxxxxxxxx>
> > ---
> > 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