virtio: add subsections to the migration stream

There is a need to add some more fields to VirtIODevice that should be
migrated (broken status, endianness). The problem is that we do not
want to break compatibility while adding a new feature... This issue has
been addressed in the generic VMState code with the use of optional
subsections. As a *temporary* alternative to port the whole virtio
migration code to VMState, this patch mimics a similar subsectionning
ability for virtio.

Since each virtio device is streamed in its own section, the idea is to
stream subsections between the end of the device section and the start
of the next sections. This allows an older QEMU to complain and exit
when fed with subsections:

Unknown savevm section type 5
Error -22 while loading VM state

All users of virtio_load()/virtio_save() need to be patched because the
subsections are streamed AFTER the device itself.

Suggested-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
virtio-net: migrate subsections

Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
virtio-blk: migrate subsections

Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
virtio-scsi: migrate subsections

Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
virtio-serial: migrate subsections

Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
virtio-balloon: migrate subsections

Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
virtio-rng: migrate subsections

While we are here, we also check virtio_load() return value.

Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
virtio: add endian-ambivalent support to VirtIODevice

Some CPU families can dynamically change their endianness. This means we
can have little endian ppc or big endian arm guests for example. This has
an impact on legacy virtio data structures since they are target endian.
We hence introduce a new property to track the endianness of each virtio
device. It is reasonnably assumed that endianness won't change while the
device is in use : we hence capture the device endianness when it gets
reset.

Of course this property must be part of the migration stream as most of
the virtio code will depend on it. It is hence migrated in a subsection
to preserve compatibility with older migration streams. The tricky part
is that the endianness gets known quite late and we must ensure no access
is made to virtio data before that. It is for example invalid to call
vring_avail_idx() as does the actual migration code: the VQ indexes sanity
checks had to be moved from virtio_load() to virtio_load_subsections()
because of that.

In fact, we have two conditions where the endianness property is stale:
- from initialization time (virtio_init) to first reset time (virtio_reset)
- from incoming migration time (virtio_load) to the time the property
  is restored (virtio_load_device_endian)
We enforce some paranoia by making the endianness a 3-value enum so
that we can poison it when it should not be used.

Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
cpu/virtio: introduce CPUClass::virtio_is_big_endian()

<disclaimer>
Legacy virtio devices are target endian, which means it depends on the CPU.
This design flaw has been commented over and over. And yes, it leads to
software boundary *violations* like the present patch. Even the topic in
the subject is affected as I could not decide between virtio and cpu :)
</disclaimer>

If we want to support targets that can change endianness (modern PPC and ARM
for the moment), we need to add a per-CPU class method to be called from
the virtio code. The virtio_ prefix in the name is a hint for people to
avoid misusage (aka. anywhere but from the virtio code).

Suggested-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
virtio: sample the guest real endianness

When the guest resets the device, we have current_cpu and we use it
to sample the guest endianness.

Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
virtio: memory accessors for endian-ambivalent targets

This is the virtio-access.h header file taken from Rusty's "endian-ambivalent
targets using legacy virtio" patch. It introduces helpers that should be used
when accessing vring data or by drivers for data that contains headers.
The virtio config space is also target endian, but the current code already
handles that with the virtio_is_big_endian() helper. There is no obvious
benefit at using the virtio accessors in this case.

Now we have two distinct paths: a fast inline one for fixed endian targets,
and a slow out-of-line one for targets that define the new TARGET_IS_BIENDIAN
macro.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
[ relicensed virtio-access.h to GPLv2+ on Rusty's request,
  pass &address_space_memory to physical memory accessors,
  per-device endianness,
  virtio tswap16 and tswap64 helpers,
  Greg Kurz <gkurz@linux.vnet.ibm.com> ]
Cc: Cédric Le Goater <clg@fr.ibm.com>
Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
virtio: allow byte swapping for vring

Quoting original text from Rusty: "This is based on a simpler patch by Anthony
Liguouri".

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
[ add VirtIODevice * argument to most helpers,
  Greg Kurz <gkurz@linux.vnet.ibm.com> ]
Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
Reviewed-by: Thomas Huth <thuth@linux.vnet.ibm.com>
virtio-net: use virtio wrappers to access headers

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Reviewed-by: Anthony Liguori <aliguori@us.ibm.com>
[ pass VirtIODevice * to memory accessors,
  TCP checksums fix by Cédric Le Goater,
  Greg Kurz <gkurz@linux.vnet.ibm.com> ]
Cc: Cédric Le Goater <clg@fr.ibm.com>
Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
virtio-balloon: use virtio wrappers to access page frame numbers

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Reviewed-by: Anthony Liguori <aliguori@us.ibm.com>
[ pass VirtIODevice * to memory accessors,
  Greg Kurz <gkurz@linux.vnet.ibm.com> ]
Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
virtio-blk: use virtio wrappers to access headers

Note that st*_raw and ld*_raw are effectively replaced by st*_p and ld*_p.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Reviewed-by: Anthony Liguori <aliguori@us.ibm.com>
[ pass VirtIODevice * to memory accessors,
  Greg Kurz <gkurz@linux.vnet.ibm.com> ]
Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
virtio-scsi: use virtio wrappers to access headers

Note that st*_raw and ld*_raw are effectively replaced by st*_p and ld*_p.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Reviewed-by: Anthony Liguori <aliguori@us.ibm.com>
[ pass VirtIODevice * to memory accessors,
  fix missing tswap32 in virtio_scsi_push_event() by Cédric Le Goater,
  Greg Kurz <gkurz@linux.vnet.ibm.com> ]
Cc: Cédric Le Goater <clg@fr.ibm.com>
Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
virtio-serial-bus: use virtio wrappers to access headers

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Reviewed-by: Anthony Liguori <aliguori@us.ibm.com>
[ pass VirtIODevice * to memory accessors,
  Greg Kurz <gkurz@linux.vnet.ibm.com> ]
Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
virtio-9p: use virtio wrappers to access headers

Note that st*_raw and ld*_raw are effectively replaced by st*_p and ld*_p.

Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
target-ppc: enable virtio endian ambivalent support

Since we cache endianness when the guest resets the
device, we rely on the current endian mode of
the cpu that does the reset.

Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>