On Thu, Aug 31, 2023 at 03:57:01PM +0300, Avihai Horon wrote:
> VFIO migration is not compatible with postcopy migration. A VFIO device
> in the destination can't handle page faults for pages that have not been
> sent yet.
>
> Doing such migration will cause the VM to crash in the destination:
>
> qemu-system-x86_64: VFIO_MAP_DMA failed: Bad address
> qemu-system-x86_64: vfio_dma_map(0x55a28c7659d0, 0xc0000, 0xb000,
> 0x7f1b11a00000) = -14 (Bad address)
> qemu: hardware error: vfio: DMA mapping failed, unable to continue
>
> To prevent this, block VFIO migration with postcopy migration.
>
> Reported-by: Yanghang Liu <yangh...@redhat.com>
> Signed-off-by: Avihai Horon <avih...@nvidia.com>
> ---
> hw/vfio/migration.c | 22 ++++++++++++++++++++++
> 1 file changed, 22 insertions(+)
>
> diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
> index 71855468fe..20994dc1d6 100644
> --- a/hw/vfio/migration.c
> +++ b/hw/vfio/migration.c
> @@ -335,6 +335,27 @@ static bool vfio_precopy_supported(VFIODevice *vbasedev)
>
> /* ---------------------------------------------------------------------- */
>
> +static int vfio_save_prepare(void *opaque, Error **errp)
> +{
> + VFIODevice *vbasedev = opaque;
> +
> + /*
> + * Snapshot doesn't use postcopy, so allow snapshot even if postcopy is
> on.
> + */
> + if (runstate_check(RUN_STATE_SAVE_VM)) {
> + return 0;
> + }
Just purely curious: will it really work to save a snapshot for the GPU
assigned use case?
> +
> + if (migrate_postcopy_ram()) {
> + error_setg(
> + errp, "%s: VFIO migration is not supported with postcopy
> migration",
> + vbasedev->name);
> + return -EOPNOTSUPP;
> + }
> +
> + return 0;
> +}
--
Peter Xu
