Re: [PATCH v5 5/7] vfio/migration: Change vIOMMU blocker from global to per device

[Joao Martins <joao.m.martins@oracle.com>]

On 30/06/2023 08:36, Zhenzhong Duan wrote:
> vIOMMU migration blocker can be consolidated to per device default
> blocker, then some vIOMMU global blocker related functions and data
> could be removed.
> 
Perhaps expand to something like below on the why it justifies the consolidation:

Contrary to multiple device blocker which needs to consider already-attached
devices to unblock/block dynamically, the vIOMMU migration blocker is a device
specific config. Meaning it only needs to know whether the device is bypassing
or not the vIOMMU (via machine property, or per pxb-pcie::bypass_iommu), and
does not need the state of currently present devices. For this reason, the
vIOMMU global migration blocker can be consolidated into the per-device
migration blocker, allowing us to remove some unnecessary code.

> This change also makes vfio_mig_active() more accurate as it doesn't
> check for global blocker.
> 
Cool callout.

> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>

With above adjustment:

Reviewed-by: Joao Martins <joao.m.martins@oracle.com>

> ---
>  hw/vfio/common.c              | 51 ++---------------------------------
>  hw/vfio/migration.c           |  7 ++---
>  hw/vfio/pci.c                 |  1 -
>  include/hw/vfio/vfio-common.h |  3 +--
>  4 files changed, 7 insertions(+), 55 deletions(-)
> 
> diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> index 00fef5aa08be..a8439447b990 100644
> --- a/hw/vfio/common.c
> +++ b/hw/vfio/common.c
> @@ -362,7 +362,6 @@ bool vfio_mig_active(void)
>  }
>  
>  static Error *multiple_devices_migration_blocker;
> -static Error *giommu_migration_blocker;
>  
>  static unsigned int vfio_migratable_device_num(void)
>  {
> @@ -420,55 +419,9 @@ void vfio_unblock_multiple_devices_migration(void)
>      multiple_devices_migration_blocker = NULL;
>  }
>  
> -static bool vfio_viommu_preset(void)
> +bool vfio_viommu_preset(VFIODevice *vbasedev)
>  {
> -    VFIOAddressSpace *space;
> -
> -    QLIST_FOREACH(space, &vfio_address_spaces, list) {
> -        if (space->as != &address_space_memory) {
> -            return true;
> -        }
> -    }
> -
> -    return false;
> -}
> -
> -bool vfio_block_giommu_migration(VFIODevice *vbasedev, Error **errp)
> -{
> -    int ret;
> -
> -    if (giommu_migration_blocker ||
> -        !vfio_viommu_preset()) {
> -        return true;
> -    }
> -
> -    if (vbasedev->enable_migration == ON_OFF_AUTO_ON) {
> -        error_setg(errp,
> -                   "Migration is currently not supported with vIOMMU enabled");
> -        return false;
> -    }
> -
> -    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_migration_finalize(void)
> -{
> -    if (!giommu_migration_blocker ||
> -        vfio_viommu_preset()) {
> -        return;
> -    }
> -
> -    migrate_del_blocker(giommu_migration_blocker);
> -    error_free(giommu_migration_blocker);
> -    giommu_migration_blocker = NULL;
> +    return vbasedev->group->container->space->as != &address_space_memory;
>  }
>  
>  static void vfio_set_migration_error(int err)
> diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
> index 09fa4714a085..80509958f0d3 100644
> --- a/hw/vfio/migration.c
> +++ b/hw/vfio/migration.c
> @@ -883,9 +883,10 @@ bool vfio_migration_realize(VFIODevice *vbasedev, Error **errp)
>          return ret;
>      }
>  
> -    ret = vfio_block_giommu_migration(vbasedev, errp);
> -    if (!ret) {
> -        return ret;
> +    if (vfio_viommu_preset(vbasedev)) {
> +        error_setg(&err, "%s: Migration is currently not supported "
> +                   "with vIOMMU enabled", vbasedev->name);
> +        return vfio_block_migration(vbasedev, err, errp);
>      }
>  
>      trace_vfio_migration_realize(vbasedev->name);
> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
> index 31c4ab250fbe..c2cf7454ece6 100644
> --- a/hw/vfio/pci.c
> +++ b/hw/vfio/pci.c
> @@ -3255,7 +3255,6 @@ static void vfio_instance_finalize(Object *obj)
>       */
>      vfio_put_device(vdev);
>      vfio_put_group(group);
> -    vfio_migration_finalize();
>  }
>  
>  static void vfio_exitfn(PCIDevice *pdev)
> diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h
> index b3014ece2edf..3c18572322fc 100644
> --- a/include/hw/vfio/vfio-common.h
> +++ b/include/hw/vfio/vfio-common.h
> @@ -227,7 +227,7 @@ extern VFIOGroupList vfio_group_list;
>  bool vfio_mig_active(void);
>  bool vfio_block_multiple_devices_migration(VFIODevice *vbasedev, Error **errp);
>  void vfio_unblock_multiple_devices_migration(void);
> -bool vfio_block_giommu_migration(VFIODevice *vbasedev, Error **errp);
> +bool vfio_viommu_preset(VFIODevice *vbasedev);
>  int64_t vfio_mig_bytes_transferred(void);
>  void vfio_reset_bytes_transferred(void);
>  
> @@ -254,6 +254,5 @@ int vfio_spapr_remove_window(VFIOContainer *container,
>  
>  bool vfio_migration_realize(VFIODevice *vbasedev, Error **errp);
>  void vfio_migration_exit(VFIODevice *vbasedev);
> -void vfio_migration_finalize(void);
>  
>  #endif /* HW_VFIO_VFIO_COMMON_H */