Re: [PATCH v6 31/36] vfio/migration: Add x-migration-multifd-transfer VFIO property

["Cédric Le Goater" <clg@redhat.com>]

On 3/4/25 23:03, Maciej S. Szmigiero wrote:
> From: "Maciej S. Szmigiero" <maciej.szmigiero@oracle.com>
> 
> This property allows configuring whether to transfer the particular device
> state via multifd channels when live migrating that device.
> 
> It defaults to AUTO, which means that VFIO device state transfer via
> multifd channels is attempted in configurations that otherwise support it.
> 
> Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>


Reviewed-by: Cédric Le Goater <clg@redhat.com>

Thanks,

C.


> ---
>   hw/vfio/migration-multifd.c   | 18 +++++++++++++++++-
>   hw/vfio/pci.c                 |  8 ++++++++
>   include/hw/vfio/vfio-common.h |  2 ++
>   3 files changed, 27 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/vfio/migration-multifd.c b/hw/vfio/migration-multifd.c
> index bfb9a72fa450..aacddc503bb8 100644
> --- a/hw/vfio/migration-multifd.c
> +++ b/hw/vfio/migration-multifd.c
> @@ -476,18 +476,34 @@ bool vfio_multifd_transfer_supported(void)
>   
>   bool vfio_multifd_transfer_enabled(VFIODevice *vbasedev)
>   {
> -    return false;
> +    VFIOMigration *migration = vbasedev->migration;
> +
> +    return migration->multifd_transfer;
>   }
>   
>   bool vfio_multifd_setup(VFIODevice *vbasedev, bool alloc_multifd, Error **errp)
>   {
>       VFIOMigration *migration = vbasedev->migration;
>   
> +    if (vbasedev->migration_multifd_transfer == ON_OFF_AUTO_AUTO) {
> +        migration->multifd_transfer = vfio_multifd_transfer_supported();
> +    } else {
> +        migration->multifd_transfer =
> +            vbasedev->migration_multifd_transfer == ON_OFF_AUTO_ON;
> +    }
> +
>       if (!vfio_multifd_transfer_enabled(vbasedev)) {
>           /* Nothing further to check or do */
>           return true;
>       }
>   
> +    if (!vfio_multifd_transfer_supported()) {
> +        error_setg(errp,
> +                   "%s: Multifd device transfer requested but unsupported in the current config",
> +                   vbasedev->name);
> +        return false;
> +    }
> +
>       if (alloc_multifd) {
>           assert(!migration->multifd);
>           migration->multifd = vfio_multifd_new();
> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
> index 89d900e9cf0c..6d6f889f59c5 100644
> --- a/hw/vfio/pci.c
> +++ b/hw/vfio/pci.c
> @@ -3377,6 +3377,9 @@ static const Property vfio_pci_dev_properties[] = {
>                       VFIO_FEATURE_ENABLE_IGD_OPREGION_BIT, false),
>       DEFINE_PROP_ON_OFF_AUTO("enable-migration", VFIOPCIDevice,
>                               vbasedev.enable_migration, ON_OFF_AUTO_AUTO),
> +    DEFINE_PROP_ON_OFF_AUTO("x-migration-multifd-transfer", VFIOPCIDevice,
> +                            vbasedev.migration_multifd_transfer,
> +                            ON_OFF_AUTO_AUTO),
>       DEFINE_PROP_BOOL("migration-events", VFIOPCIDevice,
>                        vbasedev.migration_events, false),
>       DEFINE_PROP_BOOL("x-no-mmap", VFIOPCIDevice, vbasedev.no_mmap, false),
> @@ -3433,6 +3436,11 @@ static void vfio_pci_dev_class_init(ObjectClass *klass, void *data)
>       pdc->exit = vfio_exitfn;
>       pdc->config_read = vfio_pci_read_config;
>       pdc->config_write = vfio_pci_write_config;
> +
> +    object_class_property_set_description(klass, /* 10.0 */
> +                                          "x-migration-multifd-transfer",
> +                                          "Transfer this device state via "
> +                                          "multifd channels when live migrating it");
>   }
>   
>   static const TypeInfo vfio_pci_dev_info = {
> diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h
> index 961931d9f457..04b123a6c929 100644
> --- a/include/hw/vfio/vfio-common.h
> +++ b/include/hw/vfio/vfio-common.h
> @@ -91,6 +91,7 @@ typedef struct VFIOMigration {
>       uint64_t mig_flags;
>       uint64_t precopy_init_size;
>       uint64_t precopy_dirty_size;
> +    bool multifd_transfer;
>       VFIOMultifd *multifd;
>       bool initial_data_sent;
>   
> @@ -153,6 +154,7 @@ typedef struct VFIODevice {
>       bool no_mmap;
>       bool ram_block_discard_allowed;
>       OnOffAuto enable_migration;
> +    OnOffAuto migration_multifd_transfer;
>       bool migration_events;
>       VFIODeviceOps *ops;
>       unsigned int num_irqs;
>