Re: [PATCH v16 QEMU 13/16] vfio: Add function to start and stop dirty pages tracking

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

On Wed, 25 Mar 2020 02:39:11 +0530
Kirti Wankhede <kwankhede@nvidia.com> wrote:

> Call VFIO_IOMMU_DIRTY_PAGES ioctl to start and stop dirty pages tracking
> for VFIO devices.
> 
> Signed-off-by: Kirti Wankhede <kwankhede@nvidia.com>
> ---
>  hw/vfio/migration.c | 36 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 36 insertions(+)
> 
> diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
> index ab295d25620e..1827b7cfb316 100644
> --- a/hw/vfio/migration.c
> +++ b/hw/vfio/migration.c
> @@ -9,6 +9,7 @@
>  
>  #include "qemu/osdep.h"
>  #include "qemu/main-loop.h"
> +#include <sys/ioctl.h>
>  #include <linux/vfio.h>
>  
>  #include "sysemu/runstate.h"
> @@ -296,6 +297,32 @@ static int vfio_load_device_config_state(QEMUFile *f, void *opaque)
>      return qemu_file_get_error(f);
>  }
>  
> +static int vfio_start_dirty_page_tracking(VFIODevice *vbasedev, bool start)
> +{
> +    int ret;
> +    VFIOContainer *container = vbasedev->group->container;
> +    struct vfio_iommu_type1_dirty_bitmap dirty = {
> +        .argsz = sizeof(dirty),
> +    };
> +
> +    if (start) {
> +        if (vbasedev->device_state & VFIO_DEVICE_STATE_SAVING) {
> +            dirty.flags = VFIO_IOMMU_DIRTY_PAGES_FLAG_START;
> +        } else {
> +            return 0;
> +        }
> +    } else {
> +            dirty.flags = VFIO_IOMMU_DIRTY_PAGES_FLAG_STOP;
> +    }

Dirty logging and device saving are logically separate, why do we link
them here?

Why do we return success when we want to start logging if we haven't
started logging?

> +
> +    ret = ioctl(container->fd, VFIO_IOMMU_DIRTY_PAGES, &dirty);
> +    if (ret) {
> +        error_report("Failed to set dirty tracking flag 0x%x errno: %d",
> +                     dirty.flags, errno);
> +    }
> +    return ret;
> +}
> +
>  /* ---------------------------------------------------------------------- */
>  
>  static int vfio_save_setup(QEMUFile *f, void *opaque)
> @@ -330,6 +357,11 @@ static int vfio_save_setup(QEMUFile *f, void *opaque)
>       */
>      qemu_put_be64(f, migration->region.size);
>  
> +    ret = vfio_start_dirty_page_tracking(vbasedev, true);
> +    if (ret) {
> +        return ret;
> +    }
> +

Haven't we corrupted the migration stream by exiting here?  Maybe this
implies the entire migration fails, therefore we don't need to add the
end marker?  Thanks,

Alex

>      qemu_put_be64(f, VFIO_MIG_FLAG_END_OF_STATE);
>  
>      ret = qemu_file_get_error(f);
> @@ -346,6 +378,8 @@ static void vfio_save_cleanup(void *opaque)
>      VFIODevice *vbasedev = opaque;
>      VFIOMigration *migration = vbasedev->migration;
>  
> +    vfio_start_dirty_page_tracking(vbasedev, false);
> +
>      if (migration->region.mmaps) {
>          vfio_region_unmap(&migration->region);
>      }
> @@ -669,6 +703,8 @@ static void vfio_migration_state_notifier(Notifier *notifier, void *data)
>          if (ret) {
>              error_report("%s: Failed to set state RUNNING", vbasedev->name);
>          }
> +
> +        vfio_start_dirty_page_tracking(vbasedev, false);
>      }
>  }
>