virtio DMA API, yet again

This switches virtio to use the DMA API on Xen and if requested by module option.

This fixes virtio on Xen, and it should break anything because it's off by default on everything except Xen PV on x86.

To the Xen people: is this okay? If it doesn't work on other Xen variants (PVH? HVM?), can you submit follow-up patches to fix it?

To everyone else: we've waffled on this for way too long. I think we should to get DMA API implementation in with a conservative policy like this rather than waiting until we achieve perfection. I'm tired of carrying these patches around.

Michael, if these survive review, can you stage these in your tree? Can you also take a look at tools/virtio? I probably broke it, but I couldn't get it to build without these patches either, so I'm stuck.

Changes from v4:
- Bake vring_use_dma_api in from the beginning.
- Automatically enable only on Xen.
- Add module parameter.
- Add s390 and alpha DMA API implementations.
- Rebase to 4.5-rc1.

Changes from v3:
- More big-endian fixes.
- Added better virtio-ring APIs that handle allocation and use them in virtio-mmio and virtio-pci.
- Switch to Michael's virtio-net patch.

Changes from v2:
- Fix vring_mapping_error incorrect argument

Changes from v1:
- Fix an endian conversion error causing a BUG to hit.
- Fix a DMA ordering issue (swiotlb=force works now).
- Minor cleanups.

Andy Lutomirski (7):
vring: Introduce vring_use_dma_api()
virtio_ring: Support DMA APIs
virtio: Add improved queue allocation API
virtio_mmio: Use the DMA API if enabled
virtio_pci: Use the DMA API if enabled
vring: Use the DMA API on Xen
vring: Add a module parameter to force-enable the DMA API

Christian Borntraeger (3):
dma: Provide simple noop dma ops
alpha/dma: use common noop dma ops
s390/dma: Allow per device dma ops

 arch/alpha/kernel/pci-noop.c        |  46 +---
 arch/s390/Kconfig                   |   6 +-
 arch/s390/include/asm/device.h      |   6 +-
 arch/s390/include/asm/dma-mapping.h |   6 +-
 arch/s390/pci/pci.c                 |   1 +
 arch/s390/pci/pci_dma.c             |   4 +-
 drivers/virtio/Kconfig              |   2 +-
 drivers/virtio/virtio_mmio.c        |  67 ++----
 drivers/virtio/virtio_pci_common.h  |   6 -
 drivers/virtio/virtio_pci_legacy.c  |  42 ++--
 drivers/virtio/virtio_pci_modern.c  |  61 ++----
 drivers/virtio/virtio_ring.c        | 412 ++++++++++++++++++++++++++++++------
 include/linux/dma-mapping.h         |   2 +
 include/linux/virtio.h              |  23 +-
 include/linux/virtio_ring.h         |  35 +++
 lib/Makefile                        |   1 +
 lib/dma-noop.c                      |  75 +++++++
 tools/virtio/linux/dma-mapping.h    |  17 ++
 18 files changed, 568 insertions(+), 244 deletions(-)
 create mode 100644 lib/dma-noop.c
 create mode 100644 tools/virtio/linux/dma-mapping.h

2.5.0