On 3/25/26 02:00, David Matlack wrote: > On 2026-03-24 09:07 PM, Yi Liu wrote: >> 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 <[email protected]> >>> Signed-off-by: David Matlack <[email protected]> >>> --- >>> 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/[email protected]/ > Thanks for the link. > Based on the discussion in the follow-up threads, I think the only check > in that function that is needed on top of what is in this patch to > ensure group immutability is this one: > /* > * The device could be considered to be fully isolated if > * all devices on the path from the device to the host-PCI > * bridge are protected from peer-to-peer DMA by ACS. > */ > if (!pci_acs_path_enabled(pdev, NULL, REQ_ACS_FLAGS)) > return false; > However, this would restrict Live Update support to only device > topologies that have these flags enabled. I am not yet sure if this > would be overly restrictive for the scenarios we care about supporting. yes. It's a bit different from that thread in which not only require singleton group but also need to be immutable. > An alternative way to ensure immutability would be to block adding > devices at probe time. i.e. Fail pci_device_group() if the device being > added has liveupdate_incoming=True, or if the group already contains a > device with liveupdate_{incoming,outgoing}=True. We would still need the > check in pci_liveupdate_preserve() to pretect against setting > liveupdate_outgoing=True on a device in a multi-device group. this looks good to me. But you'll disallow hotplug-in during liveupdate. not sure about if any decision w.r.t. hotplug. is it acceptable? BTW. A question not specific to this patch. If failure happens after executing kexec, is there any chance to fallback to the prior kernel? Regards, Yi Liu
