Re: [PATCH v3 09/10] vfio/migration: Don't block migration device dirty tracking is unsupported

[Cédric Le Goater]

On 7/8/24 4:34 PM, Joao Martins wrote:
> By default VFIO migration is set to auto, which will support live
> migration if the migration capability is set *and* also dirty page
> tracking is supported.
>
> For testing purposes one can force enable without dirty page tracking
> via enable-migration=on, but that option is generally left for testing
> purposes.
>
> So starting with IOMMU dirty tracking it can use to acomodate the lack of
> VF dirty page tracking allowing us to minimize the VF requirements for
> migration and thus enabling migration by default for those.
>
> Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
> ---
>   hw/vfio/migration.c | 6 +++++-
>   1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
> index 34d4be2ce1b1..89195928666f 100644
> --- a/hw/vfio/migration.c
> +++ b/hw/vfio/migration.c
> @@ -1012,6 +1012,7 @@ void vfio_reset_bytes_transferred(void)
>    */
>   bool vfio_migration_realize(VFIODevice *vbasedev, Error **errp)
>   {
> +    HostIOMMUDeviceClass *hiodc = HOST_IOMMU_DEVICE_GET_CLASS(vbasedev->hiod);
>       Error *err = NULL;
>       int ret;
>   
> @@ -1036,7 +1037,10 @@ bool vfio_migration_realize(VFIODevice *vbasedev, Error **errp)
>           return !vfio_block_migration(vbasedev, err, errp);
>       }
>   
> -    if (!vbasedev->dirty_pages_supported) {
> +    if (!vbasedev->dirty_pages_supported &&
> +        (vbasedev->iommufd &&


I don't think we need to check ->iommufd. The class handler below will
return false for the vfio/legacy backend.

Thanks,

C.



> +         !hiodc->get_cap(vbasedev->hiod,
> +                         HOST_IOMMU_DEVICE_CAP_DIRTY_TRACKING, NULL))) {
>           if (vbasedev->enable_migration == ON_OFF_AUTO_AUTO) {
>               error_setg(&err,
>                          "%s: VFIO device doesn't support device dirty 
> tracking",