On Mon, 20 Oct 2014 18:08:56 +0200
Alexander Graf <ag...@suse.de> 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.
>
This is a follow-up to the following commit:
commit e43c0b2ea5574efb0bedebf6a7d05916eefeba52
Author: Michael S. Tsirkin <m...@redhat.com>
Date: Thu Sep 11 18:45:33 2014 +0200
virtio-pci: enable bus master for old guests
The goal was to support *again* buggy guests that do DMA without
enabling bus master, since QEMU now uses the bus master address
space for delivering MSI/MSI-x messages.
We were missing some bits to support cross version migration.
Thanks to Michael's patch, I could migrate a buggy RHEL 6.5 guest
from QEMU v2.1 to QEMU master.
>
> Alex
>
Cheers.
--
Greg
