Re: [PATCH v6 05/12] PCI: liveupdate: Keep bus numbers constant during Live Update

[Samiullah Khawaja <skhawaja@google.com>]

On Fri, May 22, 2026 at 08:24:03PM +0000, David Matlack wrote:
>During a Live Update, preserved devices must be allowed to continue
>performing memory transactions so the kernel cannot change the fabric
>topology, including bus numbers, since that would require disabling
>and flushing any memory transactions first.
>
>To keep bus numbers constant, always inherit the secondary and
>subordinate bus numbers assigned to bridges during scanning, instead of
>assigning new ones, if any PCI devices are being preserved. Note that
>the kernel inherits bus numbers even on bridges without any downstream
>endpoints that were preserved. This avoids accidentally assigning a
>bridge a new window that overlaps with a preserved device that is
>downstream of a different bridge.
>
>If a bridge is scanned with a broken topology or has no bus numbers
>set during a Live Update, refuse to assign it new bus numbers and refuse
>to enumerate devices below it until the Live Update is finished. This is
>a safety measure to prevent topology conflicts.
>
>Require that CONFIG_CARDBUS is not enabled to enable
>CONFIG_PCI_LIVEUPDATE since inheriting bus numbers on PCI-to-CardBus
>bridges requires additional work but is not a priority at the moment.
>
>Signed-off-by: David Matlack <dmatlack@google.com>
>---
> .../admin-guide/kernel-parameters.txt         |  6 +-
> drivers/pci/Kconfig                           |  2 +-
> drivers/pci/liveupdate.c                      | 83 ++++++++++++++++++-
> drivers/pci/liveupdate.h                      | 14 ++++
> drivers/pci/probe.c                           | 17 +++-
> include/linux/pci_liveupdate.h                |  4 +
> 6 files changed, 119 insertions(+), 7 deletions(-)
>

Reviewed-by: Samiullah Khawaja <skhawaja@google.com>