Re: [PATCH v3 11/13] vfio/migration: Block migration with vIOMMU

[Alex Williamson]

On Sat,  4 Mar 2023 01:43:41 +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>
> ---
>  hw/vfio/common.c              | 51 +++++++++++++++++++++++++++++++++++
>  hw/vfio/migration.c           |  6 +++++
>  include/hw/vfio/vfio-common.h |  2 ++
>  3 files changed, 59 insertions(+)
> 
> diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> index 5b8456975e97..9b909f856722 100644
> --- a/hw/vfio/common.c
> +++ b/hw/vfio/common.c
> @@ -365,6 +365,7 @@ bool vfio_mig_active(void)
>  }
>  
>  static Error *multiple_devices_migration_blocker;
> +static Error *giommu_migration_blocker;
>  
>  static unsigned int vfio_migratable_device_num(void)
>  {
> @@ -416,6 +417,56 @@ void vfio_unblock_multiple_devices_migration(void)
>      multiple_devices_migration_blocker = NULL;
>  }
>  
> +static unsigned int vfio_use_iommu_device_num(void)
> +{
> +    VFIOGroup *group;
> +    VFIODevice *vbasedev;
> +    unsigned int device_num = 0;
> +
> +    QLIST_FOREACH(group, &vfio_group_list, next) {
> +        QLIST_FOREACH(vbasedev, &group->device_list, next) {
> +            if (vbasedev->group->container->space->as !=
> +                                    &address_space_memory) {
> +                device_num++;
> +            }
> +        }
> +    }
> +
> +    return device_num;
> +}

I'm not sure why we're counting devices since nobody uses that data,
but couldn't this be even more simple and efficient by walking the
vfio_address_spaces list?

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_use_iommu_device_num()) {
> +        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_use_iommu_device_num()) {
> +        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..3e75868ae7a9 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;
>  
> @@ -659,6 +664,7 @@ void vfio_migration_finalize(VFIODevice *vbasedev)
>          unregister_savevm(VMSTATE_IF(vbasedev->dev), "vfio", vbasedev);
>          vfio_migration_exit(vbasedev);
>          vfio_unblock_multiple_devices_migration();
> +        vfio_unblock_giommu_migration();

Hmm, this actually gets called from vfio_exitfn(), doesn't all the
group, device, address space unlinking happen in
vfio_instance_finalize()?  Has this actually been tested to remove the
blocker?  And why is this a _finalize() function when it's called from
an exit callback?  Thanks,

Alex

>      }
>  
>      if (vbasedev->migration_blocker) {
> diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h
> index 1cbbccd91e11..38e44258925b 100644
> --- a/include/hw/vfio/vfio-common.h
> +++ b/include/hw/vfio/vfio-common.h
> @@ -233,6 +233,8 @@ extern VFIOGroupList vfio_group_list;
>  bool vfio_mig_active(void);
>  int vfio_block_multiple_devices_migration(Error **errp);
>  void vfio_unblock_multiple_devices_migration(void);
> +int vfio_block_giommu_migration(Error **errp);
> +void vfio_unblock_giommu_migration(void);
>  int64_t vfio_mig_bytes_transferred(void);
>  
>  #ifdef CONFIG_LINUX