Re: [PATCH v2 1/1] vfio: Change default dirty pages tracking behavior during migration

[Alex Williamson <alex.williamson@redhat.com>]

On Mon, 23 Nov 2020 19:53:19 +0530
Kirti Wankhede <kwankhede@nvidia.com> wrote:

> By default dirty pages tracking is enabled during iterative phase
> (pre-copy phase).
> Added per device opt-out option 'pre-copy-dirty-page-tracking' to
> disable dirty pages tracking during iterative phase. If the option
> 'pre-copy-dirty-page-tracking=off' is set for any VFIO device, dirty
> pages tracking during iterative phase will be disabled.
> 
> Signed-off-by: Kirti Wankhede <kwankhede@nvidia.com>
> ---
>  hw/vfio/common.c              | 11 +++++++----
>  hw/vfio/pci.c                 |  3 +++
>  include/hw/vfio/vfio-common.h |  1 +
>  3 files changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> index c1fdbf17f2e6..6ff1daa763f8 100644
> --- a/hw/vfio/common.c
> +++ b/hw/vfio/common.c
> @@ -311,7 +311,7 @@ bool vfio_mig_active(void)
>      return true;
>  }
>  
> -static bool vfio_devices_all_stopped_and_saving(VFIOContainer *container)
> +static bool vfio_devices_all_saving(VFIOContainer *container)
>  {
>      VFIOGroup *group;
>      VFIODevice *vbasedev;
> @@ -329,8 +329,11 @@ static bool vfio_devices_all_stopped_and_saving(VFIOContainer *container)
>                  return false;
>              }
>  
> -            if ((migration->device_state & VFIO_DEVICE_STATE_SAVING) &&
> -                !(migration->device_state & VFIO_DEVICE_STATE_RUNNING)) {
> +            if (migration->device_state & VFIO_DEVICE_STATE_SAVING) {
> +                if ((vbasedev->pre_copy_dirty_page_tracking == ON_OFF_AUTO_OFF)
> +                    && (migration->device_state & VFIO_DEVICE_STATE_RUNNING)) {
> +                        return false;
> +                }
>                  continue;
>              } else {
>                  return false;
> @@ -1125,7 +1128,7 @@ static void vfio_listerner_log_sync(MemoryListener *listener,
>          return;
>      }
>  
> -    if (vfio_devices_all_stopped_and_saving(container)) {
> +    if (vfio_devices_all_saving(container)) {
>          vfio_sync_dirty_bitmap(container, section);
>      }
>  }
> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
> index 58c0ce8971e3..5601df6d6241 100644
> --- a/hw/vfio/pci.c
> +++ b/hw/vfio/pci.c
> @@ -3182,6 +3182,9 @@ static void vfio_instance_init(Object *obj)
>  static Property vfio_pci_dev_properties[] = {
>      DEFINE_PROP_PCI_HOST_DEVADDR("host", VFIOPCIDevice, host),
>      DEFINE_PROP_STRING("sysfsdev", VFIOPCIDevice, vbasedev.sysfsdev),
> +    DEFINE_PROP_ON_OFF_AUTO("x-pre-copy-dirty-page-tracking", VFIOPCIDevice,
> +                            vbasedev.pre_copy_dirty_page_tracking,
> +                            ON_OFF_AUTO_ON),
>      DEFINE_PROP_ON_OFF_AUTO("display", VFIOPCIDevice,
>                              display, ON_OFF_AUTO_OFF),
>      DEFINE_PROP_UINT32("xres", VFIOPCIDevice, display_xres, 0),
> diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h
> index baeb4dcff102..267cf854bbba 100644
> --- a/include/hw/vfio/vfio-common.h
> +++ b/include/hw/vfio/vfio-common.h
> @@ -129,6 +129,7 @@ typedef struct VFIODevice {
>      unsigned int flags;
>      VFIOMigration *migration;
>      Error *migration_blocker;
> +    OnOffAuto pre_copy_dirty_page_tracking;
>  } VFIODevice;
>  
>  struct VFIODeviceOps {

I applied this and sent a pull request because I think it's important
that we set the default correctly, but why use an OnOffAuto rather than
a boolean?  Is the intent that auto might make device specific
decisions?  Thanks,

Alex