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

Bjorn Helgaas
2026-03-25T23:13:52Z

On Mon, Mar 23, 2026 at 11:57:55PM +0000, 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;
> +}
> +
> +static int pci_liveupdate_validate_iommu_group(struct pci_dev *dev)
> +{
> + struct iommu_group *group;
> + int nr_devices = 0;
> +
> + group = iommu_group_get(&dev->dev);
> + if (group) {
> + iommu_group_for_each_dev(group, &nr_devices, count_devices);
> + iommu_group_put(group);
> + }
> +
> + if (nr_devices != 1) {
> + pci_warn(dev, "Live Update preserved devices must be in singleton iommu groups!");
> + return -EINVAL;
> + }
> +
> + return 0;

I assume the requirement is that there *is* an iommu_group and also
that dev is the only member. If so, I think the intent would be a
little clearer as:

group = iommu_group_get(&dev->dev);
if (!group)
goto no_group;

iommu_group_for_each_dev(group, &nr_devices, count_devices);
iommu_group_put(group);

if (nr_devices == 1) {
return 0;

no_group:
pci_warn(...);
return -EINVAL;

> +}
> +
> int pci_liveupdate_preserve(struct pci_dev *dev)
> {
> struct pci_dev_ser new = INIT_PCI_DEV_SER(dev);
> @@ -232,6 +260,10 @@ int pci_liveupdate_preserve(struct pci_dev *dev)
> if (dev->is_virtfn || dev->is_physfn)
> return -EINVAL;
>
> + ret = pci_liveupdate_validate_iommu_group(dev);
> + if (ret)
> + return ret;
> +
> guard(mutex)(&pci_flb_outgoing_lock);
>
> if (dev->liveupdate_outgoing)
> @@ -357,7 +389,7 @@ int pci_liveupdate_retrieve(struct pci_dev *dev)
> if (!dev->liveupdate_incoming)
> return -EINVAL;
>
> - return 0;
> + return pci_liveupdate_validate_iommu_group(dev);
> }
> EXPORT_SYMBOL_GPL(pci_liveupdate_retrieve);
>
> --
> 2.53.0.983.g0bb29b3bc5-goog
>