Re: [PATCH v3 03/24] PCI: Require Live Update preserved devices are in singleton iommu_groups

[Yi Liu <yi.l.liu@intel.com>]

On 3/24/26 07:57, David Matlack wrote:
> Require that Live Update preserved devices are in singleton iommu_groups
> during preservation (outgoing kernel) and retrieval (incoming kernel).
> 
> PCI devices preserved across Live Update will be allowed to perform
> memory transactions throughout the Live Update. Thus IOMMU groups for
> preserved devices must remain fixed. Since all current use cases for
> Live Update are for PCI devices in singleton iommu_groups, require that
> as a starting point. This avoids the complexity of needing to enforce
> arbitrary iommu_group topologies while still allowing all current use
> cases.
> 
> Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
> Signed-off-by: David Matlack <dmatlack@google.com>
> ---
>   drivers/pci/liveupdate.c | 34 +++++++++++++++++++++++++++++++++-
>   1 file changed, 33 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/liveupdate.c b/drivers/pci/liveupdate.c
> index bec7b3500057..a3dbe06650ff 100644
> --- a/drivers/pci/liveupdate.c
> +++ b/drivers/pci/liveupdate.c
> @@ -75,6 +75,8 @@
>    *
>    *  * The device must not be a Physical Function (PF).
>    *
> + *  * The device must be the only device in its IOMMU group.
> + *
>    * Preservation Behavior
>    * =====================
>    *
> @@ -105,6 +107,7 @@
>   
>   #include <linux/bsearch.h>
>   #include <linux/io.h>
> +#include <linux/iommu.h>
>   #include <linux/kexec_handover.h>
>   #include <linux/kho/abi/pci.h>
>   #include <linux/liveupdate.h>
> @@ -222,6 +225,31 @@ static void pci_ser_delete(struct pci_ser *ser, struct pci_dev *dev)
>   	ser->nr_devices--;
>   }
>   
> +static int count_devices(struct device *dev, void *__nr_devices)
> +{
> +	(*(int *)__nr_devices)++;
> +	return 0;
> +}
> +

there was a related discussion on the singleton group check. have you
considered the device_group_immutable_singleton() in below link?

https://lore.kernel.org/linux-iommu/20220421052121.3464100-4-baolu.lu@linux.intel.com/

Regards,
Yi Liu