[PATCH v4 08/11] PCI: liveupdate: Require preserved devices are in immutable singleton IOMMU groups

[David Matlack]

On Thu, Apr 23, 2026 at 2:23 PM David Matlack <dmatlack at google.com> wrote:
>
> Restrict support for preserving PCI devices across Live Update to
> devices in immutable singleton IOMMU groups. A device's group is
> considered immutable if all bridges upstream from the device up to the
> root port have the required ACS features enabled.
>
> Since ACS flags are inherited across a Live Update for preserved devices
> and all the way up to the root port, the preserved device should be in a
> singleton IOMMU group after kexec in the new kernel.
>
> This change should still permit all the current use-cases for PCI device
> preservation across Live Update, since it is intended to be used in
> Cloud enviroments which should have the required ACS features enabled
> for virtualization purposes.
>
> If a device is part of a multi-device IOMMU group, preserving it will
> now fail with an error. This restriction may be lifted in the future if
> support for preserving multi-device groups is desired.
>
> Signed-off-by: David Matlack <dmatlack at google.com>

Jason, do you think requiring singleton iommu groups is still
necessary/useful now that this series preserves ACS flags on preserved
devices and upstream bridges?