Re: [Qemu-devel] [PATCH v3] virtio-pci: fix migration for pci bus master

[Alexander Graf <agraf@suse.de>]

On 20.10.14 08:58, Michael S. Tsirkin wrote:
> Current support for bus master (clearing OK bit) together with the need to
> support guests which do not enable PCI bus mastering, leads to extra state in
> VIRTIO_PCI_FLAG_BUS_MASTER_BUG bit, which isn't robust in case of cross-version
> migration for the case when guests use the device before setting DRIVER_OK.
> 
> Rip out this code, and replace it:
> -   Modern QEMU doesn't need VIRTIO_PCI_FLAG_BUS_MASTER_BUG
>     so just drop it for latest machine type.
> -   For compat machine types, set PCI_COMMAND if DRIVER_OK
>     is set.
> 
> As this is needed for 2.1 for both pc and ppc, move PC_COMPAT macros from pc.h
> to a new common header.
> 
> Reviewed-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
> Tested-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
> 
> Alexander, could you pls ack me merging this?
> Thanks!

Have you tried whether this works with old kernel versions? We
introduced the broken flag for very specific old kernel versions that
got their flags wrong IIRC.


Alex