Re: [Qemu-devel] [PATCH v7 05/13] vfio: Add migration region initialization and finalize function

[Cornelia Huck <cohuck@redhat.com>]

On Tue, 9 Jul 2019 15:19:12 +0530
Kirti Wankhede <kwankhede@nvidia.com> wrote:

> - Migration functions are implemented for VFIO_DEVICE_TYPE_PCI device in this
>   patch series.
> - VFIO device supports migration or not is decided based of migration region
>   query. If migration region query is successful and migration region
>   initialization is successful then migration is supported else migration is
>   blocked.
> 
> Signed-off-by: Kirti Wankhede <kwankhede@nvidia.com>
> Reviewed-by: Neo Jia <cjia@nvidia.com>
> ---
>  hw/vfio/Makefile.objs         |   2 +-
>  hw/vfio/migration.c           | 145 ++++++++++++++++++++++++++++++++++++++++++
>  hw/vfio/trace-events          |   3 +
>  include/hw/vfio/vfio-common.h |  14 ++++
>  4 files changed, 163 insertions(+), 1 deletion(-)
>  create mode 100644 hw/vfio/migration.c
> 
(...)
> diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
> new file mode 100644
> index 000000000000..a2cfbd5af2e1
> --- /dev/null
> +++ b/hw/vfio/migration.c
> @@ -0,0 +1,145 @@
> +/*
> + * Migration support for VFIO devices
> + *
> + * Copyright NVIDIA, Inc. 2019
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2. See
> + * the COPYING file in the top-level directory.
> + */
> +
> +#include "qemu/osdep.h"
> +#include <linux/vfio.h>
> +
> +#include "hw/vfio/vfio-common.h"
> +#include "cpu.h"
> +#include "migration/migration.h"
> +#include "migration/qemu-file.h"
> +#include "migration/register.h"
> +#include "migration/blocker.h"
> +#include "migration/misc.h"
> +#include "qapi/error.h"
> +#include "exec/ramlist.h"
> +#include "exec/ram_addr.h"
> +#include "pci.h"
> +#include "trace.h"
> +
> +static void vfio_migration_region_exit(VFIODevice *vbasedev)
> +{
> +    VFIOMigration *migration = vbasedev->migration;
> +
> +    if (!migration) {
> +        return;
> +    }
> +
> +    if (migration->region.buffer.size) {
> +        vfio_region_exit(&migration->region.buffer);
> +        vfio_region_finalize(&migration->region.buffer);
> +    }
> +}
> +
> +static int vfio_migration_region_init(VFIODevice *vbasedev)
> +{
> +    VFIOMigration *migration = vbasedev->migration;
> +    Object *obj = NULL;
> +    int ret = -EINVAL;
> +
> +    if (!migration) {

You're checking for vbasedev->migration here...

> +        return ret;
> +    }
> +
> +    if (!vbasedev->ops || !vbasedev->ops->vfio_get_object) {
> +        return ret;
> +    }
> +
> +    obj = vbasedev->ops->vfio_get_object(vbasedev);
> +    if (!obj) {
> +        return ret;
> +    }
> +
> +    ret = vfio_region_setup(obj, vbasedev, &migration->region.buffer,
> +                            migration->region.index, "migration");
> +    if (ret) {
> +        error_report("%s: Failed to setup VFIO migration region %d: %s",
> +                     vbasedev->name, migration->region.index, strerror(-ret));
> +        goto err;
> +    }
> +
> +    if (!migration->region.buffer.size) {
> +        ret = -EINVAL;
> +        error_report("%s: Invalid region size of VFIO migration region %d: %s",
> +                     vbasedev->name, migration->region.index, strerror(-ret));
> +        goto err;
> +    }
> +
> +    return 0;
> +
> +err:
> +    vfio_migration_region_exit(vbasedev);
> +    return ret;
> +}
> +
> +static int vfio_migration_init(VFIODevice *vbasedev,
> +                               struct vfio_region_info *info)
> +{
> +    int ret;
> +
> +    vbasedev->migration = g_new0(VFIOMigration, 1);

...but always allocate it before calling the function above here. What
am I missing?

> +    vbasedev->migration->region.index = info->index;
> +
> +    ret = vfio_migration_region_init(vbasedev);
> +    if (ret) {
> +        error_report("%s: Failed to initialise migration region",
> +                     vbasedev->name);
> +        return ret;

It feels a bit odd that you don't free ->migration again here, but
delay it until finalize.

> +    }
> +
> +    return 0;
> +}
> +
> +/* ---------------------------------------------------------------------- */
> +
> +int vfio_migration_probe(VFIODevice *vbasedev, Error **errp)
> +{
> +    struct vfio_region_info *info;
> +    Error *local_err = NULL;
> +    int ret;
> +
> +    ret = vfio_get_dev_region_info(vbasedev, VFIO_REGION_TYPE_MIGRATION,
> +                                   VFIO_REGION_SUBTYPE_MIGRATION, &info);
> +    if (ret) {
> +        goto add_blocker;

So you don't even call init if the region is not present (which seems
reasonable)...

> +    }
> +
> +    ret = vfio_migration_init(vbasedev, info);
> +    if (ret) {
> +        goto add_blocker;
> +    }
> +
> +    trace_vfio_migration_probe(vbasedev->name, info->index);
> +    return 0;
> +
> +add_blocker:
> +    error_setg(&vbasedev->migration_blocker,
> +               "VFIO device doesn't support migration");
> +    ret = migrate_add_blocker(vbasedev->migration_blocker, &local_err);
> +    if (local_err) {
> +        error_propagate(errp, local_err);
> +        error_free(vbasedev->migration_blocker);
> +    }
> +    return ret;
> +}
> +
> +void vfio_migration_finalize(VFIODevice *vbasedev)
> +{
> +    if (!vbasedev->migration) {

...but you're doing a quick exit here in that case. Shouldn't you get
rid of the blocker here?

> +        return;
> +    }
> +
> +    if (vbasedev->migration_blocker) {
> +        migrate_del_blocker(vbasedev->migration_blocker);
> +        error_free(vbasedev->migration_blocker);
> +    }
> +
> +    vfio_migration_region_exit(vbasedev);
> +    g_free(vbasedev->migration);
> +}