Re: [Qemu-devel] [PATCH v9 00/22] legacy virtio support for cross-endian targets

[Greg Kurz <gkurz@linux.vnet.ibm.com>]

On Tue, 24 Jun 2014 20:25:41 +0300
"Michael S. Tsirkin" <mst@redhat.com> wrote:

> On Tue, Jun 24, 2014 at 07:06:58PM +0200, Greg Kurz wrote:
> > The current legacy virtio devices have a fundamental flaw: they all share
> > data between host and guest with guest endianness ordering. This is ok for
> > nearly all architectures that have fixed endianness. Unfortunately, it breaks
> > for recent PPC64 and ARM targets that can change endianness at runtime.
> > The virtio-1.0 specification fixes the issue by enforcing little-endian
> > ordering. It may take some time though until the code for 1.0 gets available
> > and supported, and all the users can migrate. There have been discussions
> > for some monthes about supporting such oddity: now we have little-endian
> > PPC64 distros available, it is worth to propose something.
> > 
> > This patch set brings legacy virtio support for cross-endian targets. The
> > rationale is that we add a new device_endianness property to VirtIODevice.
> > This property is used as a runtime indicator to decide wether we should
> > do little-endian or big-endian conversion, as opposed to the compile time
> > choice we have now with TARGTE_WORDS_BIGENDIAN.
> 
> typo :) no need to repost for this.
> 

heh :) :) thanks !

> > The choice was made to
> > sample the device endianness out of the endianness mode of the guest
> > CPU that does the reset. It is an evil but logical consequence of the
> > initial flaw in the virtio specification, and it was agreed that the concept
> > would be a good common base for ARM and PPC64 enablement at least. Please
> > note also that this new property is state and must be preserved across
> > migrations.
> > 
> > There are several parts in the serie:
> > - patches 1 and 2 are simple fixes
> > - patches 3 to 9 introduce VMState based subsections in the virtio
> >   migration code. This is needed because we introduce a new property
> >   in VirtIODevice that we want to migrate without ruining compatibility
> >   efforts
> > - patches 10 to 13 bring virtio device endianness and memory accessors
> >   to be used by the virtio code
> > - patches 14 to 20 wire the new memory accessors everywhere accross the
> >   virtio code
> > - patch 21 is the PPC64 enablement
> > - patch 22 is a follow-up workaround to disable vhost-net acceleration
> >   in the case the host and guest have different endianness, because
> >   it is not supported for the moment
> > 
> > Changes since v8 are provided in each patch.
> > 
> > Cheers.
> > 
> > ---
> > 
> > Alexander Graf (1):
> >       virtio-serial: don't migrate the config space
> > 
> > Cédric Le Goater (1):
> >       virtio-net: byteswap virtio-net header
> > 
> > Greg Kurz (14):
> >       virtio: introduce device specific migration calls
> >       virtio-net: implement per-device migration calls
> >       virtio-blk: implement per-device migration calls
> >       virtio-serial: implement per-device migration calls
> >       virtio-balloon: implement per-device migration calls
> >       virtio-rng: implement per-device migration calls
> >       virtio: add subsections to the migration stream
> >       exec: introduce target_words_bigendian() helper
> >       cpu: introduce CPUClass::virtio_is_big_endian()
> >       virtio: add endian-ambivalent support to VirtIODevice
> >       virtio: memory accessors for endian-ambivalent targets
> >       virtio-9p: use virtio wrappers to access headers
> >       target-ppc: enable virtio endian ambivalent support
> >       vhost-net: disable when cross-endian
> > 
> > Rusty Russell (6):
> >       virtio: allow byte swapping for vring
> >       virtio-net: use virtio wrappers to access headers
> >       virtio-balloon: use virtio wrappers to access page frame numbers
> >       virtio-blk: use virtio wrappers to access headers
> >       virtio-scsi: use virtio wrappers to access headers
> >       virtio-serial-bus: use virtio wrappers to access headers
> > 
> > 
> >  exec.c                            |    8 -
> >  hw/9pfs/virtio-9p-device.c        |    3 -
> >  hw/block/virtio-blk.c             |   62 ++++++-----
> >  hw/char/virtio-serial-bus.c       |   94 ++++++++++------
> >  hw/net/vhost_net.c                |   19 +++
> >  hw/net/virtio-net.c               |   56 +++++++---
> >  hw/scsi/virtio-scsi.c             |   40 ++++---
> >  hw/virtio/virtio-balloon.c        |   33 +++---
> >  hw/virtio/virtio-pci.c            |   11 +-
> >  hw/virtio/virtio-rng.c            |   12 +-
> >  hw/virtio/virtio.c                |  216 ++++++++++++++++++++++++++++---------
> >  include/hw/virtio/virtio-access.h |  170 +++++++++++++++++++++++++++++
> >  include/hw/virtio/virtio.h        |   17 +++
> >  include/qom/cpu.h                 |    1 
> >  qom/cpu.c                         |    6 +
> >  target-ppc/cpu.h                  |    2 
> >  target-ppc/translate_init.c       |   15 +++
> >  17 files changed, 583 insertions(+), 182 deletions(-)
> >  create mode 100644 include/hw/virtio/virtio-access.h
> > 
> > --
> > Greg
> 



-- 
Gregory Kurz                                     kurzgreg@fr.ibm.com
                                                 gkurz@linux.vnet.ibm.com
Software Engineer @ IBM/Meiosys                  http://www.ibm.com
Tel +33 (0)562 165 496

"Anarchy is about taking complete responsibility for yourself."
        Alan Moore.