On 21.10.14 12:16, Michael S. Tsirkin wrote: > On Mon, Oct 20, 2014 at 06:08:56PM +0200, Alexander Graf wrote: >> >> >> 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 <gk...@linux.vnet.ibm.com> >>> Tested-by: Greg Kurz <gk...@linux.vnet.ibm.com> >>> Signed-off-by: Michael S. Tsirkin <m...@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 > > Yes. The point is that since 2.1 the broken flag isn't effective > anymore: when bus master is off, PCI blocks outgoing transactions and > setting internal flags isn't going to help. > > Instead, we detect a buggy guest and immediately enable bus master for > it - no need for a separate flag.
Ok, works for me then. Alex
