Re: [PATCH v5 13/15] vfio/migration: Block migration with vIOMMU

[Alex Williamson <alex.williamson@redhat.com>]

On Tue,  7 Mar 2023 12:54:48 +0000
Joao Martins <joao.m.martins@oracle.com> wrote:

> Migrating with vIOMMU will require either tracking maximum
> IOMMU supported address space (e.g. 39/48 address width on Intel)
> or range-track current mappings and dirty track the new ones
> post starting dirty tracking. This will be done as a separate
> series, so add a live migration blocker until that is fixed.
> 
> Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
> Reviewed-by: Cédric Le Goater <clg@redhat.com>
> ---
>  hw/vfio/common.c              | 46 +++++++++++++++++++++++++++++++++++
>  hw/vfio/migration.c           |  5 ++++
>  hw/vfio/pci.c                 |  1 +
>  include/hw/vfio/vfio-common.h |  2 ++
>  4 files changed, 54 insertions(+)
> 
> diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> index 2639b393a781..2b9bcf70aa36 100644
> --- a/hw/vfio/common.c
> +++ b/hw/vfio/common.c
> @@ -362,6 +362,7 @@ bool vfio_mig_active(void)
>  }
>  
>  static Error *multiple_devices_migration_blocker;
> +static Error *giommu_migration_blocker;
>  
>  static unsigned int vfio_migratable_device_num(void)
>  {
> @@ -413,6 +414,51 @@ void vfio_unblock_multiple_devices_migration(void)
>      multiple_devices_migration_blocker = NULL;
>  }
>  
> +static bool vfio_viommu_preset(void)
> +{
> +    VFIOAddressSpace *space;
> +
> +    QLIST_FOREACH(space, &vfio_address_spaces, list) {
> +        if (space->as != &address_space_memory) {
> +            return true;
> +        }
> +    }
> +
> +    return false;
> +}
> +
> +int vfio_block_giommu_migration(Error **errp)
> +{
> +    int ret;
> +
> +    if (giommu_migration_blocker ||
> +        !vfio_viommu_preset()) {
> +        return 0;
> +    }
> +
> +    error_setg(&giommu_migration_blocker,
> +               "Migration is currently not supported with vIOMMU enabled");
> +    ret = migrate_add_blocker(giommu_migration_blocker, errp);
> +    if (ret < 0) {
> +        error_free(giommu_migration_blocker);
> +        giommu_migration_blocker = NULL;
> +    }
> +
> +    return ret;
> +}
> +
> +void vfio_unblock_giommu_migration(void)
> +{
> +    if (!giommu_migration_blocker ||
> +        vfio_viommu_preset()) {
> +        return;
> +    }
> +
> +    migrate_del_blocker(giommu_migration_blocker);
> +    error_free(giommu_migration_blocker);
> +    giommu_migration_blocker = NULL;
> +}
> +
>  static void vfio_set_migration_error(int err)
>  {
>      MigrationState *ms = migrate_get_current();
> diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
> index a2c3d9bade7f..776fd2d7cdf3 100644
> --- a/hw/vfio/migration.c
> +++ b/hw/vfio/migration.c
> @@ -634,6 +634,11 @@ int vfio_migration_probe(VFIODevice *vbasedev, Error **errp)
>          return ret;
>      }
>  
> +    ret = vfio_block_giommu_migration(errp);
> +    if (ret) {
> +        return ret;
> +    }
> +
>      trace_vfio_migration_probe(vbasedev->name);
>      return 0;
>  
> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
> index 939dcc3d4a9e..30a271eab38c 100644
> --- a/hw/vfio/pci.c
> +++ b/hw/vfio/pci.c
> @@ -3185,6 +3185,7 @@ static void vfio_instance_finalize(Object *obj)
>       */
>      vfio_put_device(vdev);
>      vfio_put_group(group);
> +    vfio_unblock_giommu_migration();
>  }

Hmm, doesn't this mean we're adding the viommu migration blocker in
common code but only removing it in pci code?  Granted that only PCI
devices currently have IOMMUs, but ick.  Thanks,

Alex