Re: [PATCH v16 QEMU 08/16] vfio: Register SaveVMHandlers for VFIO device

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Kirti Wankhede (kwankhede@nvidia.com) wrote:
> Define flags to be used as delimeter in migration file stream.
> Added .save_setup and .save_cleanup functions. Mapped & unmapped migration
> region from these functions at source during saving or pre-copy phase.
> Set VFIO device state depending on VM's state. During live migration, VM is
> running when .save_setup is called, _SAVING | _RUNNING state is set for VFIO
> device. During save-restore, VM is paused, _SAVING state is set for VFIO device.
> 
> Signed-off-by: Kirti Wankhede <kwankhede@nvidia.com>
> Reviewed-by: Neo Jia <cjia@nvidia.com>
> ---
>  hw/vfio/migration.c  | 76 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>  hw/vfio/trace-events |  2 ++
>  2 files changed, 78 insertions(+)
> 
> diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
> index 22ded9d28cf3..033f76526e49 100644
> --- a/hw/vfio/migration.c
> +++ b/hw/vfio/migration.c
> @@ -8,6 +8,7 @@
>   */
>  
>  #include "qemu/osdep.h"
> +#include "qemu/main-loop.h"
>  #include <linux/vfio.h>
>  
>  #include "sysemu/runstate.h"
> @@ -24,6 +25,17 @@
>  #include "pci.h"
>  #include "trace.h"
>  
> +/*
> + * Flags used as delimiter:
> + * 0xffffffff => MSB 32-bit all 1s
> + * 0xef10     => emulated (virtual) function IO
> + * 0x0000     => 16-bits reserved for flags
> + */
> +#define VFIO_MIG_FLAG_END_OF_STATE      (0xffffffffef100001ULL)
> +#define VFIO_MIG_FLAG_DEV_CONFIG_STATE  (0xffffffffef100002ULL)
> +#define VFIO_MIG_FLAG_DEV_SETUP_STATE   (0xffffffffef100003ULL)
> +#define VFIO_MIG_FLAG_DEV_DATA_STATE    (0xffffffffef100004ULL)
> +
>  static void vfio_migration_region_exit(VFIODevice *vbasedev)
>  {
>      VFIOMigration *migration = vbasedev->migration;
> @@ -126,6 +138,69 @@ static int vfio_migration_set_state(VFIODevice *vbasedev, uint32_t mask,
>      return 0;
>  }
>  
> +/* ---------------------------------------------------------------------- */
> +
> +static int vfio_save_setup(QEMUFile *f, void *opaque)
> +{
> +    VFIODevice *vbasedev = opaque;
> +    VFIOMigration *migration = vbasedev->migration;
> +    int ret;
> +
> +    qemu_put_be64(f, VFIO_MIG_FLAG_DEV_SETUP_STATE);
> +
> +    if (migration->region.mmaps) {
> +        qemu_mutex_lock_iothread();
> +        ret = vfio_region_mmap(&migration->region);
> +        qemu_mutex_unlock_iothread();
> +        if (ret) {
> +            error_report("%s: Failed to mmap VFIO migration region %d: %s",
> +                         vbasedev->name, migration->region.index,
> +                         strerror(-ret));
> +            return ret;
> +        }
> +    }
> +
> +    ret = vfio_migration_set_state(vbasedev, ~0, VFIO_DEVICE_STATE_SAVING);
> +    if (ret) {
> +        error_report("%s: Failed to set state SAVING", vbasedev->name);
> +        return ret;
> +    }
> +
> +    /*
> +     * Save migration region size. This is used to verify migration region size
> +     * is greater than or equal to migration region size at destination
> +     */
> +    qemu_put_be64(f, migration->region.size);
> +
> +    qemu_put_be64(f, VFIO_MIG_FLAG_END_OF_STATE);

OK, good, so now we can change that to something else if you want to
migrate something extra in the future.

> +    ret = qemu_file_get_error(f);
> +    if (ret) {
> +        return ret;
> +    }
> +
> +    trace_vfio_save_setup(vbasedev->name);

I'd put that trace at the start of the function.

> +    return 0;
> +}
> +
> +static void vfio_save_cleanup(void *opaque)
> +{
> +    VFIODevice *vbasedev = opaque;
> +    VFIOMigration *migration = vbasedev->migration;
> +
> +    if (migration->region.mmaps) {
> +        vfio_region_unmap(&migration->region);
> +    }
> +    trace_vfio_save_cleanup(vbasedev->name);
> +}
> +
> +static SaveVMHandlers savevm_vfio_handlers = {
> +    .save_setup = vfio_save_setup,
> +    .save_cleanup = vfio_save_cleanup,
> +};
> +
> +/* ---------------------------------------------------------------------- */
> +
>  static void vfio_vmstate_change(void *opaque, int running, RunState state)
>  {
>      VFIODevice *vbasedev = opaque;
> @@ -191,6 +266,7 @@ static int vfio_migration_init(VFIODevice *vbasedev,
>          return ret;
>      }
>  
> +    register_savevm_live("vfio", -1, 1, &savevm_vfio_handlers, vbasedev);

That doesn't look right to me;  firstly the -1 should now be
VMSTATE_INSTANCE_ID_ANY - after the recent change in commit 1df2c9a

Have you tried this with two vfio devices?
This is quite rare - it's an iterative device that can have
multiple instances;  if you look at 'ram' for example, all the RAM
instances are handled inside the save_setup/save for the one instance of
'ram'.  I think here you're trying to register an individual vfio
device, so if you had multiple devices you'd see this called twice.

So either you need to make vfio_save_* do all of the devices in a loop -
which feels like a bad idea;  or replace "vfio" in that call by a unique
device name;  as long as your device has a bus path then you should be
able to use the same trick vmstate_register_with_alias_id does, and use
I think,  vmstate_if_get_id(VMSTAETE_IF(vbasedev)).

but it might take some experimentation since this is an odd use.

>      vbasedev->vm_state = qemu_add_vm_change_state_handler(vfio_vmstate_change,
>                                                            vbasedev);
>  
> diff --git a/hw/vfio/trace-events b/hw/vfio/trace-events
> index 69503228f20e..4bb43f18f315 100644
> --- a/hw/vfio/trace-events
> +++ b/hw/vfio/trace-events
> @@ -149,3 +149,5 @@ vfio_migration_probe(char *name, uint32_t index) " (%s) Region %d"
>  vfio_migration_set_state(char *name, uint32_t state) " (%s) state %d"
>  vfio_vmstate_change(char *name, int running, const char *reason, uint32_t dev_state) " (%s) running %d reason %s device state %d"
>  vfio_migration_state_notifier(char *name, int state) " (%s) state %d"
> +vfio_save_setup(char *name) " (%s)"
> +vfio_save_cleanup(char *name) " (%s)"
> -- 
> 2.7.0
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK