Re: [PATCH RFCv2 7/8] vfio/migration: Don't block migration device dirty tracking is unsupported

[Avihai Horon <avihaih@nvidia.com>]

Hi Joao,

On 12/02/2024 15:56, Joao Martins wrote:
> External email: Use caution opening links or attachments
>
>
> 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/iommufd.c        | 3 +--
>   hw/vfio/migration.c      | 4 +++-
>   include/sysemu/iommufd.h | 1 +
>   3 files changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/hw/vfio/iommufd.c b/hw/vfio/iommufd.c
> index 697d40841d7f..78d8f4391b68 100644
> --- a/hw/vfio/iommufd.c
> +++ b/hw/vfio/iommufd.c
> @@ -275,8 +275,7 @@ static int iommufd_cdev_detach_ioas_hwpt(VFIODevice *vbasedev, Error **errp)
>       return ret;
>   }
>
> -static bool iommufd_dirty_pages_supported(IOMMUFDDevice *iommufd_dev,
> -                                          Error **errp)
> +bool iommufd_dirty_pages_supported(IOMMUFDDevice *iommufd_dev, Error **errp)
>   {
>       uint64_t caps;
>       int r;
> diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
> index 70e6b1a709f9..674e76b3f3df 100644
> --- a/hw/vfio/migration.c
> +++ b/hw/vfio/migration.c
> @@ -938,7 +938,9 @@ 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_dev.iommufd &&

Shouldn't we check the type of base_hdev instead?

> +         !iommufd_dirty_pages_supported(&vbasedev->iommufd_dev, &err))) {

Maybe we can store IOMMUFD DPT support in iommufd_dev and use it instead 
of querying it here?

Thanks.

>           if (vbasedev->enable_migration == ON_OFF_AUTO_AUTO) {
>               error_setg(&err,
>                          "%s: VFIO device doesn't support device dirty tracking",
> diff --git a/include/sysemu/iommufd.h b/include/sysemu/iommufd.h
> index bc6607e3d444..d6be49f2ac78 100644
> --- a/include/sysemu/iommufd.h
> +++ b/include/sysemu/iommufd.h
> @@ -53,6 +53,7 @@ typedef struct IOMMUFDDevice {
>   void iommufd_device_init(IOMMUFDDevice *idev);
>   int iommufd_device_get_hw_capabilities(IOMMUFDDevice *idev, uint64_t *caps,
>                                          Error **errp);
> +bool iommufd_dirty_pages_supported(IOMMUFDDevice *idev, Error **errp);
>   int iommufd_backend_alloc_hwpt(int iommufd, uint32_t dev_id,
>                                  uint32_t pt_id, uint32_t flags,
>                                  uint32_t data_type, uint32_t data_len,
> --
> 2.39.3
>