@samitouri / QOSamiQemu / commits / 4435853689

hw/arm/smmuv3-accel: Enforce viommu association when CMDQV is active

When CMDQV is active, the first cold-plugged VFIO device establishes the viommu to host SMMUv3 association, and the guest's boot-time CMDQV configuration (VINTFs, VCMDQs) is built on top of that association. Hot-unplugging that device would release the viommu and tear down all CMDQV state. Hot-plugging another device behind a different host SMMUv3+CMDQV would then re-bind the same vSMMUv3 to new host hardware, while the guest keeps using its boot-time configuration and ends up issuing commands to the wrong host. Block hot-unplug of the establishing device to avoid this; retaining the binding across unplug is non-trivial and not required by any current use case. Also abort at machine_done if cmdqv=on is requested but no cold-plugged VFIO device was present to initialize it. Reviewed-by: Nicolin Chen <nicolinc@nvidia.com> Tested-by: Nicolin Chen <nicolinc@nvidia.com> Reviewed-by: Eric Auger <eric.auger@redhat.com> Signed-off-by: Shameer Kolothum <skolothumtho@nvidia.com> Tested-by: Eric Auger <eric.auger@redhat.com> Message-id: 20260609112552.378999-30-skolothumtho@nvidia.com Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

Shameer Kolothum committed Jun 9, 2026 at 12:25 UTC 4435853689e245a8bfec9eb92fd84f3904d60d47

2 files changed +19

hw/arm/smmuv3-accel.c

+18

@@ -759,6 +759,18 @@ static bool smmuv3_accel_set_iommu_device(PCIBus *bus, void *opaque, int devfn,

759 return false;

760 }

761

762 + /*

763 + * CMDQV is active: block hot-unplug of the device that established the

764 + * viommu association. Removing it would cause the vIOMMU to host SMMUv3

765 + * association be changed via device hot-plug.

766 + */

767 + if (s->s_accel->cmdqv_ops) {

768 + PCIDevice *pdev = pci_find_device(bus, pci_bus_num(bus), devfn);

769 + error_setg(&accel_dev->unplug_blocker,

770 + "CMDQV is active: removing the device that established the "

771 + "viommu association would break the guest CMDQV");

772 + qdev_add_unplug_blocker(DEVICE(pdev), accel_dev->unplug_blocker);

773 + }

774 done:

775 accel_dev->hiodi = hiodi;

776 accel_dev->s_accel = s->s_accel;

@@ -1082,6 +1094,12 @@ static void smmuv3_accel_machine_done(Notifier *notifier, void *data)

1094 "at least one cold-plugged VFIO device");

1095 exit(1);

1096 }

1097 +

1098 + if (s->cmdqv == ON_OFF_AUTO_ON && !accel->cmdqv) {

1099 + error_report("arm-smmuv3 cmdqv=on requires at least one cold-plugged "

1100 + "VFIO device");

1101 + exit(1);

1102 + }

1103 }

1104

1105 bool smmuv3_accel_init(SMMUv3State *s, Error **errp)

hw/arm/smmuv3-accel.h

@@ -84,6 +84,7 @@ typedef struct SMMUv3AccelDevice {

84 IOMMUFDVdev *vdev;

85 QLIST_ENTRY(SMMUv3AccelDevice) next;

86 SMMUv3AccelState *s_accel;

87 + Error *unplug_blocker; /* set when CMDQV is active to block hot-unplug */

88 } SMMUv3AccelDevice;

90 bool smmuv3_accel_init(SMMUv3State *s, Error **errp);